Aaahhh! Male cardinal tetras Ooohhh! Who asked this?
Yes they do.
Depending on their sizes, yes.
The problem will not be the tetras coexisting with the Bettas. It will be the female Betta. She will undoubtedly be killed by the male. He may well spawn her first but afterwards, if she is left in his presence he will kill her. Also if he has ova or fry to look after he will kill the tetras in defence of his young.
yes
Yes provided the tank is large enough and properly maintained with a good filter and weekly water changes of 50%. To avoid problems from overstocking, you will need at least 1 gallon of water for each 1 inch of fish length.
Yes, they are all tetras and should get along fine.
Cardinal Tetras are from the very tropical, acid waters of the Amazonian Rainforest. Almost any small fish species that comes either from the same area or places that have similar water conditions should be OK with them. The species that come to mind are most Tetras, Danios, Barbs, Rasboras, Corydoras, and most of the Dwarf Amazonian Cichlids like Rams etc.
yes
You can NOT keep female and male bettas together! Male bettas can get very aggressive and will fight to the death. Make sure to separate your bettas.
rams, cardinal and rummynose tetras, corydoras, and BN plecos those are the best, there are a few other, but take caution
Yes I'm fairly certain. I have 1cardinal and 4 neons and they all swim together...
When a female Betta is introduced to a male Betta one of two things will happen. The male will build a bubble nest and try to spawn the female and during the courting time he will drive off any other occupants of the tank and kill them if they can not escape (hide successfully). He does this in order to protect his prospective young. If she fails to spawn he will drive her off and kill her if she is not removed. In other words you can not keep a male Betta with another Betta (male or female) without trouble. The Tetras will be perfectly OK with a Betta female OR a Betta male. Not the two (pair) that you are proposing. The general rule that all experienced and successfull aquarists live by is a fish needs 1 gallon of water per inch of body length. Work it out.