Hello and welcome to the forums!
As every one has kindly pointed out it would be best to seperate your lovely fish and keep them in individual tanks. When kept in a tank together they'll likely get very stressed out. If keeping a male and female together they will likely either fight or spawn - and if they spawn they'll still be aggressive to one another and get hurt and more stressed, there's also the added stress on you
as there would probably be a lot of babies to raise (and this costs an awful lot).
In the wild bettas live in stillwater ponds with lots of plant life, my reading tells me that they can actually move from pond to pond in search of new territory. They are your "lone ranger" of the fish world and really do prefer to be kept alone.
I have read (although cannot confirm this through scientific documentation) that bettas were introduced into rice paddies by man to help control pest insect populations. Regardless of whether or not this is true those rice paddies are very shallow but very, very wide. It's quite possible that bettas entered the rice paddies looking for more territory and found them to be ideal. Bettas breathe air like we do and so shallow water is usually better - but that doesn't mean a small tank is always better.
Your 1.5 gallon aquariums will be fine for long-term care of your fish, as long as you only have one fish per tank and do two weekly water changes: one 50% and one 100% (including draining the tank and cleaning all the tank substrate, whether sand, gravel or stones). It'll be even better for your fish if you can ensure their water temperature is between 76 and 82 degrees F, this is their normal temperature range -- but this can wait if you don't have the facility to provide extra heating. What matters right now is ensuring that each of your fish lives on their own and that they aren't in constant view of each other.
I hope all continues to go well - it sounds like you're doing okay so far -- and thank you for coming to the forums to ask about this. It's great to see another person who is willing to learn about these gorgeous animals and someone who isn't afraid to ask questions.