If I were you, I would find the beta a mason jar for a few days to see what happens with the oto. The apple snail might eat the eggs but most likely not all of the them and once they hatch, the snail will be no danger to the fry. But 2 mason jars would fix that problem as well. I am keeping my fingers crossed for both of you.
20g L46/hastatus/pygmy corys, 10g OEBTs, 10g blue bees/blue velvet shrimp, 10g CRS, 25g L174s/BNs/L340s, 10g yellow/red tiger shrimp, 15g clown plecos/CPDs/habrosus corys, 15g cory fry, 29g Weitzmani/panda corys/BNs, 46g L134s/salt and pepper corys/BNs/rubberlip pleco, 55g SAE/L201s/L199s/BNs/kissing gourami, 75g L316s/BNs/L134s/CAE/silver dollar, 30g L340s/L211s/CPDs,10g tangerine tiger/snowball shrimp, 20g L134/habrosus corys, 10g CPD fry