One rabbit is round, the other is thin! What to do!

Hello!
So I have a polish dwarf and a lion head. Both smaller breeds, but of course the polish is the smallest. My polish seems to be gaining weight, his stomach is about an inch off of the ground. He is pretty active, but I have not been home enough to let him out. So far, I have not tried just giving him more time out of his cage. It is just so hard to catch someone who is so small and fast! The Lion head actually had GI stasis last winter and since then, he really hasn't put the weight back on that he lost. I feed him twice a day hoping that will help him and i feed the polish a little less food to try to help him lose weight. I also noticed I've been giving the polish the same amount I gave the Lion head, there is a 2 pound difference with them. I just wanted to see if there are things I could try before going to the vet. The polish has a lot of energy and is non stop. So i believe he is healthy, just needs a bit of help with the weight.

[ScarletSorrows]

my dwarf long hair bun bun is fairly thin so to help him put on weight i got food that has more weight to it and i got a little mini pet feeder and placed it inside the cage and when i let him out to play i leave the cage open so he has access to his foor 24hrs a day. he seems to have gained some weight since then. and as for the fat bun bun i would try feeding him diet food maybe something a little lighter cut back on treats and plenty of time to run and play!