Need a home for this kitten

Need a home for this little guy, we live in an apartment complex and found him crying outside a neighbors unit, asked the neighbor if that was their cat and their only response was “yeah it’s our sisters but we don’t want it anymore so we just put it outside.” I would love to take him in but we have three cats including one kitten that we’re already trying to get our older cats adjusted too and i think it would be too much. Any help would be much appreciated. p.s. he’s extremely friendly, and came right to us when we went back out to check on him.