Thanks for all the suggestions, guys!

I picked up the Frontline last night and applied it to each of them. The package states that it's fine ofr kittens 8 weeks and older, and so far my little Julio hasn't shown any signs of reaction.

As far as feeding time goes, I may have to just feed once a day and put them in separate rooms during that time. Marley's on Feline CD for urinary tract disease, so it's important that he stick to that diet. Likewise, Marley's food is too acidic for Julio's little system. I know they won't be happy if they can't graze all day, but maybe when Julio gets older the vet can help me find a food they can both tolerate.

How do you multi-cat moms handle the litterbox situation? Do you recommend two separate boxes? When it was just Marley I had one covered box that I did a complete litter change with several times a week using liners....no scooping. Can I keep this routine and just add a second litterbox next to the first?