Unsure what to do with "abandoned" kitten and upset mother.

Hi folks! Just looking for some input on what feels like a no-win situation.

Long story short, I moved into a new neighborhood a few months ago, and it came with a big feral cat population that I started feeding. Tonight, one of them brought a baby with her -- and left it. I brought it inside, and waited to see if she'd return with more, but she didn't.

Now, many hours later, the mother is back outside, crying and looking for it. There's just a few problems, so I'm unsure what to do.

Problem 1: This baby is about 4 weeks old, so it's definitely too small to be away from its mom. I'm experienced with bottle feeding, but the mom seems very upset and isn't leaving our porch. So it feels like a good idea to give it back.

Problem 2: This is a wooded area. The neighborhood is overrun by aggressive raccoons. I've been attacked by them when I went out at night, so I'm surprised any cats survive at all. Giving the kitten back will make the mom happy, but may be dooming it to a worse fate.

Problem 3: I have an extremely beloved elderly cat, who screams and hisses at the stray cats when she sees them through our glass door. The obvious solution here would be to bring the stray mom inside as well, but with my living situation, there's no place inside to easily separate the stray from my existing cat, and it would almost immediately lead to fights.

Problem 4: The local shelters are full. When we first moved here, I looked into getting these strays to a local rescue or shelter so they don't have to live outside, but every shelter is packed and can't take any surrenders. I'd love to take mom and baby both to a shelter in the morning, but it's not an option.

Sorry for the length, but. What to do in this situation? If I return the baby, it'll make mom happy, but the baby will probably be killed. If I keep it, the poor mom is too upset. It feels like there's no good choice, so I'd love folks to give some rational input to help me lol.