We really need some advice

[germanman]

Ok let me start off with saying we made one huge mistake and it has lead to only nightmares but I'd like to only have advice/ideas regarding the question...because we already deeply regret the mistake of getting our leos from ***** and keeping the tank where the cats can be around them. To give a bit of background we got 3 leos from ***** and a bit after 2 started to waste away, vets found nothing...neither did my looks under the scope at home, we tried Albon and several other products anyway as well as "force feeding". Sadly one of the two died and the other is on its way out but trying so hard to carry on. That being said once those were isolated we got two healthy young leos form a better pet store. They are being kept with our healthy male in a smaller plastic holder within the 39 gallon terrarium(we have very limited space). The tub is high and we didn't think the other gecko could get in and left the top off for more air. Anyway tonight i caught the cat up on top the cage and found the big male in with the young ones and one missing a tail. Before we isolated the other sick gecko its tail too went missing a few days after it looked "broken" as my Gf put it. I'm just trying to figure out if we have a tail eater or if maybe the cats scare them and they dropped the tail and the male then ate the "moving thing". Please help us we don't know what to do. I feel like such an idiot; I am a long time bird,fish,reptile keeper, and a zoology major and should have never made these mistakes. We have limited space and money...so tomorrow I will move the leo tank to the floor in our room where the cats aren't allowed (I'm allergic to cats but my Girl loves em and they were here before me).
Sorry for the wall of text but it is all such a nightmare!

Also I'm afraid the sick leo is almost gone and seems in so much pain whats the best way to euthanize it? At my work we have always severed the spine or froze sick/dieing animals...it just seems so cruel for a pet we love!