Wow, Pam, that is quite the conundrum. I have read that in order for a cat to be on a diet, you really do have to keep the food closely monitored, and with a bunch of kitties, that can be a challenge.

The only suggestion I could come up with is let your sister keep LOC, since she only has two cats, and you take one of the ones she has. This arrangement would allow LOC to get his weight down, and save you from being cat-apulted from the recliner.