Don't get too upset -- feeding a horse properly for their jobs and health issues has gotten to be an overwhelming issue in this day and age.
You say they are both hot and overweight. For sure ditch the alfalfa and ditch the oats too
They probably don't need all the protein they're getting from the alfalfa and the oats are chuck full of starch a/k/a bad fat calories. My 17 yo IR horse is so sensitive to alfalfa that even 1/4 cup shoots his insulin up. The 25 yo EMS horse, however, gets 1-1/2 lbs of soaked timothy/alfalfa cubes and has to have the extra protein the alfalfa provides him. MSM
is great for any inflammatory issues. Brewers Yeast
is what my vet recommends for the digestive tract. Unless the horse has serious ulcer issues, like one of my metabolic horse's has, then it's on to more serious remedies than Brewer's yeast. Omega-3 Horseshine
(flax) is great for hoof and coat health; you can find that at Tractor Supply. It's pricey but I only feed 1/2 cup daily to the Walkers and 3/8 cup daily to the little Arab (he's 13.3H)
A 20 lb bag lasts five weeks, feeding three horses.
In terms of getting their vitamins/minerals into them, research the top brands of ration balancers in your area. Triple Crown's is called "30%", Purina's is called "Enrich 32" for example.
I am surrounded by Purina, Co-op feed, and Nutrena, so I drive 40 miles to buy Triple Crown - lollol But that's all a matter of preference
The best thing to try and do is apply the KISS principle where possible: "Keep It Simple Stupid". I try and try and try but with two metabolic horses that are always needing something changed in their diet because they change, I can't get past "Keep" lol lol lol
Regarding hay --- if you aren't in an area where your hay crop has been damaged by drought, by the best quality mixed grass hay you can find.
Quality starts with at least being weed-free which, more often than not, cow hay is not. You won't really know about the vit/min makeup of the hay until you buy and send it for testing <---that's another eye-popper that's probably best left for another "over whelming" conversation
So bottom line from my perspective (others will have their own suggestions): Keep
MSM, Brewers Yeast Ditch
Alfalfa, oats Add,
a good ration balancer to be sure they get their vit/min, good grass hay, and Omega-3 Horseshine, if you can afford it.
Hope this helps.