For 8,17 you do come in the way you think is obvious. You are right that you need the same amount of ice between the cats and the exits. That level contains everything you need to make that happen (except for one spare cat you'll have to bring with you - I don't think you have enough range of motion otherwise, at least I never found a way without it).
For 13,8, you're actually on the right track when you realized that you can't get past the wall. If you push the only rock you can push, it blocks the hallway. But you do have to get on the other side of the rock. So if you can't pass the rock, the rock has to pass you. You're going to spend a lot of time carefully moving the revived cat around. MetaMetaPuzzle gave you the key here, although to restate - a 0-flag doesn't have to kill you.