In regex syntax, "$" indicates the end of the string. In your regex, you are trying to remove any character after the end of the string which is not a number or a dot, which won't work, so the "," is never removed from your string, resulting in a conversion error.
You can do this:

new BigDecimal(row1.Trade_Amount.replaceAll("[^\\d.]", ""))

Assuming I've understood your question correctly, you just want to instantiate a BigDecimal from a String, in which case:

new BigDecimal(TalendDate.formatDate("yyyyMMddHHmmss",
                        TalendDate.parseDate("yyyy-MM-dd HH:mm:ss",row5.StopTime)))

You can use BigDecimal

BigDecimal v1 = new BigDecimal("15.25");
BigDecimal v2 = new BigDecimal("5.25");
BigDecimal v3 = new BigDecimal("1.15");

BigDecimal v123 = v1.divide(v2, MathContext.DECIMAL64).multiply(v3);

System.out.println(v123);
System.out.println(v123.setScale(2, RoundingMode.HALF_UP));

prints

3.34047619047619075
3.34

To perform this calculation using double

double v1 = 15.25;
double v2 = 5.25;
double v3 = 1.15;
double v123 = v1 / v2 * v3;
System.out.println(v123);
System.out.printf("%.2f%n", v123);

prints

3.34047619047619
3.34

If MathContext.DECIMAL128 had been used, the unrounded value would be

3.340476190476190476190476190476191

and in this example, both solutions are more than accurate enough.