Awesome!
I wish I had direct experience to be able to give you better advice. However, all I can do is offer what i've read or heard:
1) I have heard of folks, specifically in California, growing pawpaws in pots. I think most rules around growing trees in pots would apply to pawpaws. Namely, you might want some kind of root-pruning setup, either air-pruning or using a coating like Microkote. Also, pawpaws have a strong taproot and in nurseries are most commonly grown in 14-inch deep pots (though some like Forest Keeling use air-pruning pots for a shallow taproot). Just something to be aware of. Hale and Hines nursery here in Tennessee sells really really big containerized pawpaws, and I believe theirs fruit with no problems. However, pawpaws are generally not mentioned in context of container growing.
2) I think you would be fine to plant 2 in a large hole. I have read references to this with pawpaws. In the wild, they grow in pretty dense patches.
3) I have been advised that mounds are not ideal for pawpaws, but who knows. As for clay, most sources say pawpaws like a looser soil with lots of organic matter (don't amend the planting hole of course). But that's probably just something that gets copied and pasted. I have some clay (not sure how it would rank on a clay "scale") and the trees i planted a few months ago seem ok. Of course, it's very early.
Not a lot of authoritative info there but maybe something to chew on. Good luck!