Give the one who was not on mum plenty of colustrum, I would say 3 days if you can get it, prob eqv to 2 feeds of your 2 quarts....or split it into more feeds but similar volume, or 10% of body weight.
Buy a really good milk replacer, follow directions and split feed over 2 feeds at least, I would prob do 3 for first week.
I do not give mine anything else, so is a bit of a crap shoot as could have been exposed to anything in yards.
The colustrum, if good quality from a good cow, should help them keep most things at bay. No point vaccinating too early from what we do down here, if you follow the directions, you prob cant go far wrong.
Hydration is important, as is getting nutrient, so good milk replacer in adequate amounts should keep you busy for a few weeks and give you time to work out what else to do relevant to your area.
I do not think if from sale barn would be much different if handed from your neighbor, apart from being able to find out history etc of parents and property...