my mom had her male betta for 8 years, he lived in one of those vases with a lilly growing out the top. He was one of the longest living we ever had in the house. He always came to the sides when we came near and he was always extremely healthy, so I say if you care for them right they can live in very small quarters just fine. My mom changed his water all the time and we don't use nets for our fish, just wet our hands and grab the fish, eventually they just let you pick them up, its great. I do this with my discus now when needed.
I myself bred bettas downstairs for years, mostly in 10g tanks with no filtration and about 2 inches of water (for breeding purposes, very well taken care of). I also had my main betta in my 75 gallon tank for 3 years with many different fish so I say they are very adaptable just watch them closely and decide for yourself. That said I have only had one pair of male bettas live together in the 75 gallon for a few years and that was only by accident, they will normally kill each other!!