Cat on special food, coming into house with other cats, what to do?

I adopted a cat recently from someone who had a baby and had to give him away. He had kidney stones in the past and so he is on Medi-cal Preventative Formula Food. He's a himalayan so they are susceptable to oxalate kidney stones. I'm taking him home for the holidays to my mom's house, however she has 5 cats. I'm wondering if I can let him roam the house considering he is on special food, and shouldn't be eating the other cats food. Any idea on how I can let him roam without having him eat the other cats food? If there wasn't so many cats, it'd be easier to control. Please help, I really don't want to always have to keep him locked up in one room all the time.