My brother passed away recently he never married, a 21year old has come forewod claiming to be his son my brothers name is not on his birth certificate. 5 year ago my brother asked the mother to get dna to prove he was his son she declined. He is now claiming the house, money and everything how will he prove who he is.

Which state?

First, my condolences on your loss.

Did your brother leave a will? In either case, his estate needs to be probated. The claimant will have to then make a claim through the probate court. The court will order a DNA test, probably billing the estate.

And yes, ANY question about law needs to include your general area as laws vary.