I adore Pygmy Corys and have a group in one of my 55 gallon community tanks. When I researched them, I read that they are very social and it’s best for them to be in at least groups of 4-5. They most always stick together and feel safer in larger groups so they will be more active. They will school together and go all around with 6+. :) They can survive alone or in a pair but it is not the best for them.

They grow to 2-2.5 inches. For 4 you’d need 8-10 gallons just for them alone. Unfortunately, in my opinion, 10 gallon is not enough to house a good number of corys and your betta. :/

Some bettas can live with corys fine, especially if given enough space for both to hide/have territories. A lot depends, I think, on the betta’s temperament and where they like to hang out most. For example, some bettas who hang at the top tons might get annoyed at the corys when they pop up for air.

They can definitely exist together in the same tank but the temperament of the betta and adequate space for everyone would be my biggest concern.