[Baz]

Type something up on paper...."...as your uncle I feel getting a tattoo at this point in your life is an unnecessary expense and will have financial repercussions for you down the road..yada yada" Date it...sign it...have him sign it.

Tell him you will keep this on file in case he ever approaches you for financial assistance.

As far as the wife, SIL, and Bf.....tell them you have documented this as a financial mistake and will keep this on file...they are on their own to do what them want in supporting the kid.

Tough love.....