Weanlings need to be separated by 4-6 months. It's weird he wants to get rid of them so fast. It's just a weird situation. Does the colt have papers? Is he registered? Is the stallion or the broodmare proven? What is the intended discipline for the horse?
I wouldn't buy another colt to be the colt's "mate". Then you have two colts instead of one. Show horse babies are fine on their own, or if you can find a boarding stable with other younger horses, put them out together.
That being said, it depends on your experience level. Colts are an entirely different animal from an adult horse, a weanling is a different animal, a yearling is a different animal, a two-year old is a different animal, etc. I would say if you have a lot of experience breaking 2 year olds, or have a good trainer on your side, you could go for it.
That being said, feed and hay are your best bets. I don't like the idea of weaning at 3 months, could stunt the growth of the foal. But I'm not a vet. :/