Ditto on the blanketing, otherwise you're feeding all those calories into thin air with shivering. When a horse is as thin as yours is, he can't regulate his body heat, PERIOD. Think of little old folks who smear on Ben Gay and wear heavy sweaters when it's 85 F outside and complain about how cold they are all the time. Most of them are just skin stretched over their bones, like your horse.
I actually like to have 2 blankets per horse, with a liner and a sheet so you can add and subtract layers as the weather dictates. Since you're where it's snowing, I'd buy each a nice, waterproof heavyweight blanket with a hood or neck rug. If you have 2 blankets per horse, if there's a wet storm and they soak through (most 'waterproof' blankets are good up to about 3 days of wet storm in my experience) you can change to a dry one and not let the horse develop a chill. More toward spring, I'd buy a liner and a waterproof sheet, that way when it's warmer, but still not warm enough, you can put the liner under the sheet and they'll stay dry and warm. For a horse in good weight, wind and cold aren't such a big thing but wet and cold are killers. For an emaciated horse, cold can be bad enough. I'll add some links to my favorite blanket line so you can see what I'm talking about. Just fyi, I've found these blankets to be the most durable and nicest on the market for the money. The only things I've found better are blankets that were $300 when I bought them 15 years ago. Since horses are VERY destructive, I don't buy $300 blankets anymore.
I'm not crazy about the feed regimen. I'm ok with the SafeChoice but I really have no use for sweet feed, it' like feeding a kid a KitKat Bar, IMO! I'd give them more SafeChoice and cut the sweet feed entirely. I would add Empower by Nutrena, it's very high fat and high calorie without being huge on the starch. I'd also add 1 oz fine white salt to their feed, 2X/day and they would get less picky about the water in a hurry. Give them a little time, they may not understand what warmed, clean water is, they just know drinking out of puddles (if they were reeeeeeallly neglected and it sounds like they were, why give them water if you don't feed 'em? That's probably what their old owner thought anyhow).
And a personal rant, which you can feel free to ignore if you like, COFFEE CANS instead of weighing or using quart scoops, in which case I STILL weigh their feed. Coffee cans can leave too much to interpretation. In my grocery store I can think of at least 3 sizes of 'large' coffee cans, which one are you using? The 5 lb one or the 2.5 lb one? And small coffee cans, is it 10 oz, 12 oz, or 14 oz? For an emaciated horse getting fed with the wrong coffee can, can be disastrous. If you read the feeding directions on the bags of feed they either adivise feeding a percentage of weight or a range in pounds, of feed for desired outcome. Coffee cans do not fit in there at all because 5 lbs of Safe Choice is not the same as 5 lbs of sweet feed and fed in the same 5 lb can you will get 3 lbs (just an example) of Safe Choice and 7 lbs of sweet feed due to density and shape of feed. Please buy yourself a hanging scale (like fishermen use) and weigh an empty bucket and then add the amount of feed you should be feeding.
Good luck & God Bless you for taking in these 2 poor babies, they are very lucky to have you! StormShield® 1680D EURO EXTREME Turnouts in Euro Fit at Schneider Saddlery
This is my favorite blanket & sheet for the money. They have a guarantee and Schnieder's tack stands behind their products 100%. They wash up like a dream and so far, I still have the first one of these I ever bought, probably 5 years ago. Don't go by the warmth guide, they are for horses in good weight. Buy the heavyweight or extra heavyweight blanket and a liner. Later in the season, I'd buy a sheet from the same line.
Occasionally, their manufacturer will mess up something pretty inconsequential and you can save big money. This liner is an example. It got made of a 'noisy' nylon, stiffer and crinklier than the soft, silent one that was supposed to be used. For the money, my horses could learn to live with it! Adjusta-Fit "Crinkly" V-Free