The first is definitely not a trivial ask. I don't know how feasible it is, but it would take a huge rewrite at the very least. And it's very reasonable to assume that such a system would allow actors 1 + 2 and 1 + 3 as separate "teams", but that would be an even harder case, at least if actor 1 can call the dualtech (actor 1's skill menu would have to list the skill twice, and the skill menu kinda doesn't allow for that. Interestingly, that's actually a supported scenario in the current plugin so long as actor 1 can't call the dualtech, since one person not in the tech - either actor 2 or 3 in this case - can still call it themselves and be treated as part of the tech.)
The second probably isn't feasible for a few reasons, most notably the damage calc. If there are C's and D's and so forth in a non-dualtech damage algorithm, the algorithm will always fail and return a default value of 0. So any such tech would be forced to only use A (meaning the direct user of the skill) for actor stats, or be a stat-ignoring status move, or it wouldn't work in the solo case. (Any workarounds for that one fall into the "no one-size-fits-all solution" category or would require extra work on the part of game developers.) There are other issues, but that's probably the biggest one. It seems far and away more practical to just create a solo version of the skill separately.