The catfish are in no danger at all. Fry won't kill the catfish, it's the other way round. But if the fry have some "breeder" grass or other dense plants they'll be fine. Catfish aren't very active hunters. The only problem you are likely to run into is that the FEMALE betta will more likely than not pulverize the male rather than mate. Tanks need to be kept nearly ideal chemically, temperature and hours of light to simulate mating season. If it's not just right, she'll just chew him up. So be prepared to take him out if his fins look tore up. Luckily he can live in a small bowl or glass etc. Just keep him covered, fed and partial water changes and give him time to recuperate. For that matter, even if they do successfully mate, he'll need to be removed shortly thereafter anyway. Females don't require, or want, any help babysitting. Male and female bettas never stay in the same tank long term. You can get a clear plastic basket that hangs inside the tank for him perhaps.