If you're organizing your own family collection, you are doing the one thing that most archivists wish was done to 99% of collections. So you deserve props. Have an organizational schema. Organize the collection in the way that you use it and the way that best allows you to find things. This is important if it ever gets donated to a museum or archive because 1) It's already organized! This cuts down on a lot of work. 2) Understanding how a collection was used by its creator is information in and of itself. The default schema is first what kind of document is it, second who created the document, third when was it made, but this is by no means the only way things can be organized, especially if it doesn't fit the collection. Storage is expensive, but there are things that can be prioritized. Most paper products made now are, at the very least, acid free, so you can get by with boxes and folders from an office supply store... at least for a while. The problem is, those products have a short life, and the clock is ticking. Buying from an archival supply company instead gives you a few things, first of all, products are published with their specs, so instead of "acid free" it's "pH 8.5 sodium bicarbonate buffer" which means that any acid already in your paper letters will be neutralized by the alkaline in the folders and boxes. This will extend the life of the documents, assuming no natural disasters. I suggest prioritizing folders and some permalife paper to interleave between documents where necessary. If it's in your budget, then you get boxes, also from an archival company for the same reason. All of the suppliers will have roughly the same options, but a standard archival flip-top metal edged box is the best option, and it will likely be one of the first things you see when you look at boxes on any of their websites. Personally, I only use legal length folders and boxes because you can always fit letter sized documents in a legal folder, but folding up a legal length sheet to fit in a letter sized folder is not ideal. Store the collection in a closet or home office if you can, avoid the basement or attic if you can. Suppliers to use are: Hollinger Metaledge (the de facto standard) Gaylord Archival (the other de facto standard) University Products (my source, same quality, but smaller selection and generally cheaper) Talas Archival Methods I highly suggest digitizing the collection. Scan your photographs to TIF, 600+ ppi for photographic prints, 3000+ ppi for negatives or slides. Scan documents to PDF for ease of use. Backup using the 3-2-1 method: 3 copies, 2 storage mediums (HDDs, SSDs, DVD if you must, et cetera), 1 copy off-site (the cloud is fine). More on reddit.com

I just do what you say that NARA suggests. It's the simplest solution while also being the lowest impact on the documents. Personally, I hate plasticlips, they're inconsistent and when they work, they cause just as much mechanical damage to documents as normal stainless steel clips do, or I end up needing to weed out plasticlips that are out of tolerance and have no grip, so I'm wasting money on a product that is marketed as safe for my purposes. I rarely use paperclips of any sort anymore, but when I do, I use stainless steel with a barrier slip so that the clip isn't in contact with the document. One anecdote that I remember from grad school was a discussion on paperclips. One year, the best practices will call for plasticlips, the next year, plastic coated stainless steel, and the next uncoated stainless steel with a barrier slip. The gist that my professor was getting at was, use what works, as long as it doesn't affect your document. And for me, I just make little subfolders, it seems to be the best available solution. More on reddit.com

Just to note here that Archival and Acid Free are two different terms. In bookbinding archival tape means that it can be removed without damaging. While for long term storage often acid free is a more important term. Another term here is lightfast and when we are talking about FP ink in an art context I think issues around acidity and lightfast pigments are your main points of interest. The OP makes a good point about the Platinum Iron Gall inks. They are a mix of iron gall and a standard dye based FP ink. That's why you will see the color run and a grey line remain. Unfortunately I have seen some light tests and specifically Cassis Black has very poor lightfastness. Now this doesn't surprise me because in fine art often reds are the most fugitive (color fades with light). There are some non-fugitive reds but they are mostly toxic Cadmium based colors. Now I have had some very good luck with the nano pigment inks. I have tried Roher&Klingner Lotte, Platinum Carbon Black, And DeAtramentis Document/Archive inks. Lotte is the cheapest of these inks and like the whole line is more prone to particles settling in the bottom. This ink needs to be shaken before filling. I have heard some people report issues with clogging pens. This is not my experience but I would advise loading into a pen with a good airtight seal. Like a twsbi with the screw on lid and a gasket. Platinum Carbon Black: This ink LOOKS more like the dip pen inks than any other ink. It dries with a kind of sheen and it is extremely opaque. I haven't seen sediment on the bottom of the bottle like with the R&K inks. This ink will give you a very rich black line even in a needlepoint nib. Very rich black. DeAtramentis Document Black/Archive Black: So DeA makes 2 seemingly identical inks one called Document and one called Archive. I believe that the Document line has gone through more rigorous testing in order to have that designator but in my experience I cannot tell the difference. Very good flow very reliable inks. Good color range. Because each pigment reacts to light differently you would need to actually test every color in a line of inks for lightfastness separately. Blacks will give you the least trouble while reds will be the most problematic. I think people are way too cautious around these inks. They are for fountain pens. They work. If you use your pen regularly they won't dry out or clog. Another option is to check out the IndiGraph pen which has been designed to be used with india ink. It has a little moisture bubble in the cap that keeps the nib damp when cap and apparently prevents it from drying out. It does such a good job humidifying the pen that the first few lines may write pale because so much moisture has been added to the nib if it has been capped for a couple of days. More on reddit.com

I'm sorry for your situation and either the Plat ink or Sailor Kiwa-guro would be good. Yes, archival paper would be a good idea, but you also should consider archival fibre tip pens. I know a lot of people in archival library activities use these for permanent work. The reason I say this is that no matter the paper, there won't be any spread or fuzzing of the line (can't say about bleed- or show-through). If the family member will be doing the writing, you really want the focus to be getting it on paper in the easiest, least invasive way possible. If you start having fussy problems with fountain pens, ink, etc, it is going to make a difficult moment more so. I know we're all here because of a love of fountain pens, but this moment calls for wisdom in purpose, not just automatically reaching for the nib stick. BTW, I have written materials from middle school in 1965 when I first started using fps, and this was just on regular school notebook paper and basic Sheaffer Skrip ink. It is still totally and easily readable. If you store these materials in a dark, dry place, you may be very surprised how long they will last. My best to you at a trying time, and blessings for being involved in a meaningful task. More on reddit.com