If you attempt to breed Bettas splendens in a 1 gallon tank you are doomed to fail. Sorry. The minimum sized tank to breed Bettas in successfully is around 10 gallons.
Provided the tank is large enough to house them all (1 inch of fish needs a minimum of 1 gallon of water) Guppies and Bettas should get along OK.
Normally, Bettas and Rubberlip Plecos aren't recommended to be tank mates but if you think that they are getting along fine together then that is OK.
I am assuming you mean Bettas. A male Betta needs to be kept away from all other Bettas. They can not be kept together. The male would kill at least one of the females. Then he would either breed with the living female and then kill her if she is not removed or he will try to spawn her and if she is not ready he will kill her anyway. This is how the Bettas evolved. Although they will mix with most other species OK male Bettas will not tolerate another Betta in their tank.
The basic rules are :- 1 inch of fish needs a minimum of 1 gallon of water. :- every tank needs a permanently running filter. :- every fish tank need to have at least 50% of its water changed every week. Follow those rules and you should be OK. A female Betta is about a 2 inch fish. Your 16 gallon tank will actually contain less than that because no tank is ever filled to the brim so assume it actually is holding about 14 gallons. This would give you an absolute maximum of 14 inches of fish which in the case of female Bettas would be a maximum of 7 fish. I would say a responsible stocking rate for that tank would be 5 female Bettas.
Provided there is sufficient room they will be OK. Male Bettas will only fight with other Male Bettas. Glofish are a genetically engineered form of Zebra Danio and are quite peacefull. Just remember ther rule "1 inch of fish needs a minimum of 1 gallon of water" Bettas grow to 2" Zebra Danios grow to 1.5" so you would need at least 7 gallons of water (That means you would need a 10 gallon rated tank)
noo
Some say they need a 5 gallon tank, but a 1 gallon tank should be ok if they are by theirselves.
A well set up and properly filtered 30 gallon tank would be OK.
Provided the tank is large enough two female Bettas should be OK together. Please read the following basic rules of fish keeping and follow them. :- 1 inch of fish needs a minimum of 1 gallon of water. (absolute minimum sized tank for 2 female Bettas is around 5 gals) :- Every fish tank needs a continuously running cycled filter. :- Every fish tank needs at least 50% of its water replaced every week. If you follow the above rules you will have few problems keeping fish healthy. If you fail in any of them I can guarantee that your fish will constantly be getting sick and dying.
No. A 2 Gallon tank is not realy large enough for one Betta. 1 Betta needs 3 gallons to itself. Male Bettas must not be kept with any other Bettas or they will kill each other. Female Bettas can be kept together under normal basic conditions. The basic rules of successfull fishkeeping are. :- 1 inch of fish needs at least 1 gallon of water. :- Every tank needs a constantly running cycled filter. :- Every tank needs at least 50% of its water replaced every week. If you keep the above rules and provide the fish with whatever other special parameters the species needs, they should do OK. I can guarantee that failure to provide the above basics will result in your fish constantly getting sick and will also shorten their lives considerably.
No, red tailed sharks get too large to survive in a 1 gallon fish tank. Only very smally fish such as endlers or guppies, or a betta, would be ok in a 1 gallon aquarium.
Yes they should be OK provided the tank is big enough and there is plenty of cover. You should have a minimum of 10 gallons of water for 2 female Bettas.