I'm not allowed to get a glass tank, because my parents reckon my crabs will be doomed anyway so there's no point "wasting" anymore money on them. Is there anything I can do to make the best out of the plastic tank I'm forced to use?
Since three crabs died when I was on holiday, I'm left with two

. I did have my neighbours looking after them but they didn't have a clue. I tried explaining everything as basic as I could, and I had to say some stupid things like "Just change the water once every two days." Apparently, that was already too much trouble to my mum and she said "Just change it
once a week." They did change the water everyday though, which was something I was relieved on. I think my smallest crab Pluto got attacked by Jupiter when molting, so I guess that how he died.
I keep the remaining two in separate tanks (Jupiter and Neptune). Jupiter is a pretty violent crab, and she'd bat anyone out of her way rather than climb over. She's much bigger than Neptune. I don't want them hurting or killing each other, so I had to separate them. Is this a good idea? Or should I put them back together again? Luckily I do have sand, and it's about three inches deep on both tanks.
I'd love to get an UTH, but again, dad says "It's a waste of money." They won't let me use my own money either

. I'm going to get a 25W moonglobe for another heat source. I've got a heat rock in there for humidity. I place a soaked sponge on top of the heat rock and the humidity shoots up to 80%. I guess temperature is my problem. Any other ideas?