It would be helpful if you identified the type of tree, otherwise there is no way anyone can answer your questions.

Sorry about that. I guess just an english walnut and chestnut. I am curious about generalities you could say about other varieties as well...

Well, your walnut and chestnut seedlings won't be 'runt' trees - they'll attain full size, but you may be waiting at least 10 years to see what sort of nuts they produce, and no, they won't be just like that of the 'parent' variety. They may be similar, they may be better, or they may be vastly inferior. There's no way to know, until they actually reach sufficient maturity to produce nuts - and even then it may be several years before you get a true indication of the potential productivity of your seedlings.

so, for someone like me, with only space for 1 or 2 trees, it doesn't sound worth it to gamble with an unknown.

No, and unless there are other compatible walnuts & chestnuts in the nearby vicinity, if you're going to plant two, you'd better make it two walnuts or two chestnuts, or you'll get few or no nuts. The chestnut, in particular, will require a pollenizer - and some are better than others.

Johndoug:

Never buy trees online unless you are already familiar with the nursery you are dealing with, and are satisfied about their reputation. You could also mention the name of the nursery you are considering. Someone else may have had experience with them.

If you have room for only two trees, nut trees may not be the best choice. Even the best grafted trees tend to become large specimens, and they take years to begin producing. They also require some processing off the tree, including curing and cracking, and the results can be disappointing. I had two grafted Carpathian Walnuts that grew over 30 feet tall before I realized they were wasting their space. Nuts were few and far between, and of poor quality, and the trees seemed subject to leaf diseases that made them unattractive. As far as I am concerned, nuts to the nuts unless you have a farm.

A couple of semi-dwarf fruit trees would be a better choice for a limited space.

Don Yellman, Great Falls, VA

I can't argue with anything others have said, but I'll put my 2 cents in for seedling nuts. Nut trees on their own roots, in my hands, seem a bit more durable than are grafted nuts. They'll definately take longer to bear, but in my situation the grafted ones don't seem to cut it. Chestnuts (in my hands) bear abundantly, mine are hybrids from the good-old Bear Creek Nursery (kneel and shed a few tears, they were fantastic). Same source for most of my Carpathian walnuts, they're about 15' tall and had their first nuts this year at around 10 years of age. The Carpathian, IMHO, is an attractive tree and the nuts sure are easy to 'pick'. But if space is limited, as Don said, there are more productive things to plant.