growing two hazelnut trees in one hole

Su starts with ...
Hi, I'd like to get some more information about hazelnut trees. I read the description that two trees can be planted in one hole.
1) How big will they grow if I put them in one hole?
2) Will they be more susceptible to diseases?
3) will it be difficult to prune the trees?
4) will the hazelnut tree grow in large pots (e.g. 75L or so)

I intend to keep the trees about 2.5-3m high x 2.5-3m wide all together if they are planted in one hole. Let me know what your opinions are pls.

Thanks very much.

Su says...
Thanks for your info. I had two trees and one died. Since they are not self-pollinating, I wasn't sure whether it's worth to try again or let it go. If there is not much extra space needed, I may give it one more chance. Thanks.