Betta fish issue

My sister has a betta fish in a bowl with bamboo plant there is no filter, heater or air pump he stayed in there for 7 months and I think the reason that he survived that long is that my sister usually don't feed it so there is no ammonia or nitrite and now the winter is almost coming so he must get a heater me or her can't buy a tank for him right now but I have a 30 gal tank established and housing 4 juvenile angel a pleco and 4 redeye tetra I keep my temperature between 28 and 25c is it a good idea to put him with them?
Note 2 things:
I have plant that divide the tank surface
My angels aren't good tank mates with fishes which prefers stay in tank surface

 

Can you get a good-sized breeder box that hangs inside the tank to keep the betta in?

Are you going to upgrade your angels and pleco soon? 4 angels absolutely cannot coexist in a 30 gallon tank.

 

Agree with the above! The best thing is to get a breeder box and put it inside the tank. This allows the warm water to circulate and protect the betta. In a 30 galon tank you should only have 1 however 2 would be the very max. Having 4 is bad since when they become adults and they start to pair off, they become aggressive and territorial and will harm the other fish. Also your tetras should be in a school of a minimum of 6

 

Thanks for the breeder box idea going to do that
My angels are 3 months old and the biggest one is 1 inch but I'm well aware about their behavior so I'm planning for 150gal in 4 months but there is a big chance that I can't buy it so I'm already find some good lfs to rehome them( the lfs which I bought them was awful ) and about redeyes I don't know that they like cooler water than angels when I bought them since I learned that I'm trying to rehome them so I don't buy the other 2 or more and they were doing fine and they don't show any signs of aggression (except one time that they decided to fight over my pleco cucumber and make him very angry) is it good idea to buy 2 or more?

 

Tetras do tend to be less aggressive in larger schools, however if they're stealing food from other fish it may not help with that

 

Okay thanks

 

Put him in the breeder box in the tank so far nothing happens except my angels are gather around him and making him a little nervous

 

I had to separate a fish into a breeder box for awhile, and I found that it got nervous when other fish swam under it. I put some sand and a small plant into the breeder box, and it calmed down a lot. Perhaps you could add some lightweight decorations in with the Betta to help calm him down?

 

Thanks for the tip it calms him very much and other fishes lose interest too