False paternity

My son will be 18 in June, his 16 year old girlfriend had a baby in February. They have only been dating since October, we did not know she was pregnant - she never looked pregnant! He is not the father, she doesn't claim that he is. The real father does not want to be involved and is not listed on the birth certificate, the girl listed her brother-in -law as the father instead. My son is determined to ammend the birth certificate when he turns 18 and claim himself as the father. Can I stop him? What is he doing to himself legally? Are there laws against intentional false information on a birth certificate?

i do not think a birth certificate can be ammended without a paternity test done. he is 18 and she is 16- what is he thinking. remind him of the 18 years of cs he will owe when they go their seperate ways- let him read some of these entries from people that are not biological fathers and their hardships.