First I'd take stool samples to the vet to find out what types of worms you may have and what to treat for. What makes you think the one horse has 'blood worms' aka Large Stongyles?
If your horse has a big belly and is ribby, chances are he's wormy and once you've got them dewormed properly, he may start picking up weight on his own. If he needs extra calories, then I'd feed him Purina Ultium Competition formula, it's high fat and formulated to not make them hot. Protein and fat don't make them hot, carbs (sugar, molasses) do. I feed Purina Strategy GX to my Arabians and if anyone needs extra I give them Ultium. I never feed sweet feed of any kind.