I've got to say that if your Bettas will not eat frozen brine shrimp or bloodworms, then something is wrong somewhere. I could imagine one or two picky Bettas, but that wold be rare. All of my Bettas have always eaten frozen brine shrimp and bloodworms, as have every Betta that I have ever seen going back to when I worked at a pet store in 1989. I knew a breeder back in 1989 that used to buy pounds of frozen brine shrimp every month and fed it to his fish exclusively. Frozen brine does foul the water faster than bloodworms in my experience.
If your Bettas won't eat frozen food, please tell us how you are trying to feed them?
I prefer Hikari foods, they seem better quality. I put a chunk/cube of frozen brine/bloodworms in a small sauce bowl and add a bit of water from my aged water bucket. I let it sit until the food is thawed. Then, for bloodworms, I use tweezers to pick up a few and feed them to each Betta. For brine, I suck them up with a dropper and squeeze a small portion into each jar, and then go around again and feed a second small portion.
I usually feed bloodworms on the first day after a water change, and brine on the day before a water change. I'll use freeze dried bloodworms occasionally, but not very often.