going to have to risk killing them

Other "party" will not lisen. I have to pick up a yearling and a 3 yearold who have been on pasture grass in idaho all winter no hay no nothing. They have ate trees and other stuff. I have offered to buy hay so he could introduce it but he says its a wast of money and he will just sell it. (he is in idaho - I live in utah/navada) When I go pick them up they will be put on a dirt lot and feed hay, as that is all I have here. Such a change can colic them I know but never had to do this before so what can I do to keep them safe and helthy?? (they are skinny but not to bad, I pick them up end of nexed month when I have the money to cut both since I have mares all around.

Small frequent feedings of hay.
Will they last another 6 weeks? Could you start feeding them yourself before you get them?

I would start with many small feedings of a hay that's not too rich. I'd say mid-quality grass would be best to start them out.

I'd probably start them out with 6-8 feedings of a couple of pounds each and access to plenty of fresh water.

If you notice them eating a bit and then walking away for a while before coming back (instead of bolting all the food they have access to), then I'd likely go ahead and give them free access. If they don't overstuff themselves at first, then they'll be okay with free access and not overfeeding.

if I didnt live 150 miles I would but I can't..:(

I just recently took in a draft horse who was kept on a no-forage diet, lived completely off Trotter and almost no hay.
I started with buckets of soaked 50/50 hay cubes, 2 quarts of dry cubes that were then well soaked 5 times a day to start, gradually adding in dry hay.
The soaked cubes ensures they're getting enough water. You could also try probiotics to help get their gut-flora in balance.
After a week or so my boy balanced at 3 buckets of cubes a day and about 8 flakes of hay a day.
I gradually added canola oil and ration balancer to his feeds.

my mare has been lossing lbs on the hay I have now so its poor quality and getting new hay in friday should I keep the poor hay and start them on it? Because I didnt buy it I don't know what the mix in it is.

My opinion, feeding poor hay to any horse is no good. While you don't want to overload them on nutrients - you also don't want to tax their body making it harder for them to break down their food.
I would start with the cubes personally and feed them good quality hay very gradually.

No, I wouldn't feed them the poor quality. If all you can get is the better quality, then that will be okay, you'll just have to be more careful and watch them to ensure they aren't getting too much and risking colic or founder.

The new hay that you're getting, what kind is it and do you have any idea on the nutrient content?

I've seen grass hays that had more nutrients than most alfalfa and I've seen alfalfa that had fewer nutrients than most grasses.

Just starting them off from a starved situation, the first few days I'd likely want something that wasn't much more than 10% protein, then gradually increase it over the next few days to between 15% and 18%.

I wont know untill he gets the load in himself (the person I buy from his hispanic and dosnt speak english he normaly buys diffrent mix and I pull a bail of the mix I like.