rights of a legitimate child

Hello. I need legal advice. My boyfriend's dad is dying and as 1 of the 2 legitimate sons, I want to help him get whatever he legally deserves.
His parents were married here in Davao but when Papa moved to the US after their separation, he married another woman in California. Now they are divorced, no children. Papa is back here in Pinas now and has a new querida. He has 1 child and an unborn baby with this querida and both kids carry Papa's last name. There is no will and testament that we know of at the moment.

My boyfriend, his kuya and their mom (the first wife) don't really have much so getting a lawyer will have to be our last resort.

My questions are:
1) Will my boyfriend, his kuya and their mom, being the legitimate family here in the Philippines, AUTOMATICALLY get anything without going to court?
2) Do the querida and her kids get anything when Papa dies?

From what I understand, legitimate children are entitled to 1/2 of the estate (hati sila boyfriend and kuya dun sa 1/2), then their Mom gets 1/4.. and the illegitimate children get 1/4 too.. Tama po ba?

PLEASE HELP.

Thank you!