Hello Josiah, this is Dr Emily Weaver, and I am an experienced equine vet and I hope I can help you out today.
As far as feeding your stallions goes, since you have no pasture, they would require a minimum of 1-2% of their body weight per day in hay. So for a 1000lb horse, that would be about 10-20 lbs of hay per day, divided into 2-3 feedings like you are doing. I always err on the side of more hay! It sounds like you are probably feeding enough, you could invest in a scale, or just ask how much each bale weighs when you buy it and use your best guestimate to figure out what each flake of hay weighs. Keep in mind your horses' body condition score, when you stand back and look at them, you shouldn't be able to see their ribs, but when you run your hand down there side you should be able to feel them easily. Now I know you can't really get your hands on them, but you can observe to see if they have any large fat pads on them, particularly along the top of there neck and on either side of the tail head. Hopefully you can get these guys caught soon!
What type of hay are you feeding? You say you are feeding seeds, what type and how much? You may be better off skipping the seeds/beet pulp mixture, and putting them on a balanced commercial horse feed (such as Purina, Seminole, Nutrena-just some brands to name a few) these feeds are designed to be balanced with the appropriate protein, vitamins and minerals for the horse. If they are getting plenty of good quality hay, they generally only need a small amount of a concentrate (1-2lbs/day).
As far as catching these guys, first off I would strongly encourage you to hire a professional trainer. There is an inherent risk when handling even the calmest horses, and these guys sound pretty wild and I would encourage you to use caution, I would hate for you to get hurt! That being said, my first suggestion would be to build them off a smaller corral/roundpen or stalls, something that you can enclose each of them in separately. Which it sounds like you are building a barn which is great! Get them separated into smaller spaces, and begin feeding them separately in their own spaces. Feed them their grain in large muck tub type container so that you can get close to their heads. You could try looping a rope around the base of your feed tub and while they are eating try and get the rope up and around there neck first! Then once you have them caught with the rope around the neck you would then try and halter, make sure you approach from the neck side, usually the left and use a halter that is open across the crown and slip nose in from behind with your left hand on the side of the face, and your right arm over the neck and behind the head. Does that make sense?
Another suggestion is to build a small round pen, something about 20m in diameter, and start exercising them in the pen. There are techniques you could try to get them to calm down with exercise and then approach you! I am not a horse trainer, but I have used some of the Monty Roberts techniques with my own horses before. You can find videos online to give you a place to start. Always always be careful! You may want to wear a helmet the first few times you exercise them as just a precaution from a kick until you know how they are going to react! Again I would encourage you to hire a professional trainer. Your safety is my number one concern!
I hope these suggestions help! It must be frustrating having 2 beautiful horses that you can't do anything with! I would strongly encourage you to get these guys gelded as soon as they are reasonably tame, that will just help them calm down so much more! Let me know if you have any further questions or concerns,