I was told it should be a black pen and signed by 3 witnesses.
A Will must be signed by the Will maker in front of two witnesses or more witnesses, but two is acceptanle. If it is being signed in front of a JP then the JP will be one witness and one more person is required to sign. All people signing the Will must use the same pen. This is an informal requirement but, if different pens are used, it will raise issues of whether or not the witnesses were present at the signing. There is no legal requirement to sign in black pen, though that is what most people chose. Either black or blue are OK as long as everyone uses the same pen.
A will must be procedurally correct however you fail to understand that a will must follow the reasonable understood method of inheritance and anyone who is a blood relative and who you want to disinherit , must be disinherited in a reasonable manner and not just because you want to.