I would rather go for legal advise or like Penny said ask your fiancee to visit the PAO office and enquire, because if the father totally abandoned the child, then he got nothing to do with the child anymore, the mere fact that the father still seeing his son, plus the fact he sign his birth cert I can smell a bit complication there, so my share is ask your fiancee to visit the PAO office, its free to ask a question to them like that, Good luck