It's hard to say what to suggest without knowing what you are working with. The heater, as long as the water is flowing should be fine, and if you are in a warm climate anyway or keep your house warm it'll probably hardly ever be used anyway.
I'm not sure about the two filters unless they are rather subtle it may bother the bettas. Most don't like water current, I say most because 2 out of the 3 I have had out of my house actually seemed to enjoy it and with swim directly under the water where it came out despite the rest of the 44 gallon tank having hardly any current.
Not being sure off all the measurements of your tank it's hard to say how big it it, but have you thought of maybe just having one betta in it as well as some community fish that are peaceful and that won't entice the betta to attack it? I'm not trying to discourage or anything, just offering ideas.