No. The tank is not large enough to house two female bettas. The basic fish keeping rule is "1 inch of fish needs 1 Gallon of water". A female Betta grows to around 1.5 inches so you would need at least a 3 gallon tank to house the 2 Bettas properly.
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.
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.
Bettas are agressive towards smaller fish, so neither.
10 gallon tank.
Male bettas should be kept alone. Female bettas can sometimes be kept with other fish, but in a large community tank. Bettas need their space!
Bettas are generally kept in their own private tank, since they can be quite vicious to other fish.
betta fish like at least a 1 gallon tank (nothing smaller) > They can live in a community tank but with no other bettas.
This is a BIG NO NO!! Bettas need at least 2.5 gallons of water to themselves, and if you put a male and a female together, it will most likely result with you have two dead bettas. Keep your boy and girl in separate 2.5 gallon heated tanks.
Bettas and other Anabantids like old water. I would be replacing only around half a gallon (4 pints) of its water weekly.
Male and female betta fish should not be kept in a tank together unless the tank is large enough for a female to escape attack, there is a partition or they are breeding. Males will kill the females. They are very aggressive and are not schooling fish.
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.