Step Son Sibling

My SS is 3 years old and last saw his biological mom and half brother (1years old) back in January when we had the half brother for a weekend and was taking him home; mind you, she told us that she was homeless before we took him back and it took her a half hour to 'find' a place for her and the half brother.

We regret taking him back to her and didn't just do emergency custody since she told us at that time she was homeless.

Well, bio mom got into some shit and SO got a call from CPS regarding the half brother.

My SO was told that if he wants custody, to go to the courts and was told that bio mom dad is also in line for custody too.

Now I asked my SO if he wanted me to get bio mom dad # because he didnt have a problem with SO having custody of bio mom dad 1st grandson that we think he wouldn't mind in us having the half brother also.

Now I ask bio mom sister for the #, and she was like well, I'm 2nd in line before your SO could get custody and is going to fight for that custody.

She has never met the half brother, neither has her dad, and SO and I have multiple times taken care of the half brother.

She had the decency to state that the half brother will go to family before friends, as if she was saying her own nephew isn't family to his half brother?! She doesnt even know anything about both children of her sister's and just had her 2nd child and both her kids are a year and under!

We are going to fight for custody for my SS half brother, as much of a shitty mom they have, she has always wanted the boys to be in each other's lives and thatz the main part I hope the judge will see.

Plus if my SO wasn't an idea for the half brother to be with, then why did CPS call him, ask questions about the child and their mom and tell him if he wants custody to go to the courts?!