1- Can I keep the two hatchling Eastern milks togethor?
Of course, you can...but I wouldn't. It makes feeding and monitoring who eats what, who sheds, etc. a whole lot easier if you keep them in separate cages. Plus, I think they are less stressed and settle in better if they are caged alone. You don't really want to use a real big cage for them, something small with plenty of hiding options will give the best results.
2- I'm using a 2 and 1/2 gallon tank for them, but how would I give them the proper heat source, they dont carry heat lamps or heat pads for cages that size.
If I were you, I'd get another 2 1/2 gallon tank and go to WalMart or some place like that and buy a human heating pad for $8.00 or so. You can use one pad for both tanks, because you don't want to heat the entire cage bottom, just six inches or so of one end. You want to have one cool end and one warm end, and a hide box on each end. For an Eastern Milk, I'd keep the cool end at room temperature (about 75 degrees F.) and the warm end around 85 to 87 degrees F. That gives them a good thermal gradient so they can move from one end of the cage to the other as they need to to thermoregulate. If you see that they are spending all of their time at the cool end, then lower the warm end temps by a couple of degrees. If you see they are spending all of their time at the warm end, then raise the cool end temps a degree or two. You will eventually find the combination they like.