You can use javascript test() method to validate name field. The test() method tests for a match in a string.

/^[A-Za-z\s]+$/.test(x) //returns true if matched, vaidates for a-z and A-Z and white space

or

/^[A-Za-z ]+$/.test(x)

function validate(id) {
    var regex = /^[a-zA-Z ]{2,30}$/;
    var ctrl =  document.getElemetnById(id);
    return regex.test(ctrl.value);
}

Your regular expression is broken. You've escaped the closing square bracket around the character set. Try this:

else if (/[^a-zA-Z0-9\-]/.test( stringf ))

Also, there's a lot of weird clutter in there that's annoying but not fatal: How many times do you really need to call getElementById('family') in that method? Once.

if (stringf=="")
{
    alert("Family name must be filled out");
    return false;
}
else if (stringf.length > 35)
{
    alert("Family name cannot be more than 35 characters");
    return false;
}
else if (/[^a-zA-Z0-9\-]/.test( stringf ))
{
    alert("Family name can only contain alphanumeric characters and hypehns(-)")
    return false;
}
return true;

Try Below Code

VF Code

<apex:inputtext value="{!name}" id="Name"/>
<apex:commandbutton onclick="validatenamevalue();" reRender="someId"/>

Javascript

function validatenamevalue(){
   var name = document.getElementById('{!$Component.formId.Name}').value;
   if(name == '' || name == null) {
     alert('Please enter FirstName & LastName');
   } else if((name.indexOf(' ') > 0 && name.indexOf(' ') == (name.length)-1) || !(name.indexOf(' ') > 0)) {
     alert('Please Enter Last Name');
   }
}