Finding out about ancestry?

Can anyone tell me how I can find out what children my mother had before me. My older brother has passed away two years ago and I know he didn't have the same birth name as my dad as my mom had him before she married my dad but then he took on my dads name without adoption or name change. Both my parents have passed away so i cant ask them. I want to know what my half brothers sas my mom registered him in HIS dads Suriname was on his birth certificate. Does anyone know how I can find this out without having to pay for expensive monthly subsc riptions I don't need. Thanks