ok, i dont know where you got that "at least 55 gallon" thing, but a smaller tank would work good too. but you also should take action to something like this:
ok, first off, take the female out-the males are very rough with them. second, go to your lfs-local fish store- and get a glass divider. also, we NEED info-how big is your tank? is it just like a 5 gal? i think a 10 gallon or maybe a 7 gal would work- 3.5 to 5 gallons for each betta at least. and, very, very important, DO NOT PUT ANY SAND IN THE TANK! the eggs are the size and color of sand. now, put the glass divider in the middle. the male will swim at the glass divider for a while and try to get to the female. when he stops, which could be from 1/2 an hour to a few days, he will make a bubble nest (male bettas have a special mucous that they will put in their mouths and take gulps of air to coat the air with the mucous, which will stay as bubbles, which is the bubble nest)
when it gets to a good size, oh say as big as him about, and the female is fat with eggs, take the divider out. the male will then squeeze the eggs out of the female and rush down to fertilize them, and the female will try to possible eat them, and she will eat a few, but he should go back and squeeze her again for a while for more eggs. when he is done, take the female out IMMEDIATELY, or else he will most likely kill her to stop her eating the eggs.
i know this is a lot of info, but copy-paste to keep the info or something, or simplify yourself if you would like. stick with me here
now, the male will take gulps of the eggs and blow them into the bubble nest, and will stay with the eggs, which sink, and if any of the eggs fall, he sucks them into his mouth and puts them back up. keep him in the tank until the eggs start hatching, which will be in i think 2-4 days, and take him out or he will eat the baby fish.
here i agree with cody, put them in their own little cups, whether its plastic/paper cups, or maybe a big tank, but there will be quite a few of them. now you can feed the babies infusoria or baby brine shrimp, which worked wonders for me. hope this helps and good luck!