Feeding and Kidney issues

One of my rats has severe colon issues and is at the moment having a protein rich diet so her fats are completely removed. This helps her a lot. Unfortunately, today we think we figured out that another girl in our group might have kidney disease. So she will probably need a protein poor diet (if it is indeed the kidneys, but she's been drinking a lot and peeing a lot as well). We normally feed all day with endless lab blocks, but we now need to resort to separate feeding. I've never done this before and was wondering if anyone can offer advice to make sure they are okay with this change. I want to make sure they still eat enough food because normally they snack through the day.. and now they would get a bit in the morning and evening when we can supervise.