So, my cousin is coming around Thanksgiving and has been threatening my betas safety.

A few days ago, I was texting my C, and I told him not to mess with my betas. He said that " he could all he wanted". Because 2 of the first days he is going to be hear. I'm in school, I'm worried he is going to do something to Angel, Devil, or Oasis,
My uncle and my C have taken things before, done something to make me cry, or plain just get on my nerves. I really want to protect my kids in the safest way possible, but I don't know how.
Devil and Oasis are safe in my room, which is off limits ( thank god), but Angel's 10 gallon is in the family room, which is where my U and C hang out a lot. I don't want to come home to 1,2, or 3 dead betas in their tanks. Does any one have any suggestions? I was thinking of asking my mom to take the 2 days of school before Thanksgiving off.