And its me again:You can as long as they're following the rules for Amphib Assault, i.e., they started the turn in the Inshore Box. If they're just moving there straight from the PRC Holding Box, then, no.
If I have one regular port or beachhead and I move two stacking points via sea transport to it can I still disembark units from amphibs or does that count against the same limit?
In the latter case, you're using the same port facilities to unload as the Sea Transport guys. In the former case, you're actually using the Amphibious capabilities, even if there's technically no "assault", so it takes more planning/execution, etc. At least, that's the theory.