Well the games from Tsukinomizu would be my all time favorite H-games for sure (the Naedoko Demons Ground would be my absolute favorite). They all have tentacles, and lots of them as the main theme, and a fair bit of futanari as 2nd theme. All female protagonists, and it is 2D, sex scenes is in the form of 2DCG's
https://f95zone.to/threads/lily-kni...e-crest-of-demonia-tsukinomizu-project.22576/ plenty of tentacles, less impregnation focus for sure, probably still some scene that might qualify, at least that leads to outright birth (I played Naedoko far more than any of the others so certainly remember the details of that one the best).
Naedoko Demons Ground is banned from this site though due to Rule 7. The main combat literally being fought with monsters you birth after getting impregnated by, mostly, being raped by loosing. Send me a PM if you are interested in that, and maybe I can guide you in the right direction
(I have also been making a bit of a mod for that one lately, though probably a while before that will be ready too, if ever, game is great as is already, so don't wait for it to play it)
Forget-Me-Not Gemini Fort
https://f95zone.to/threads/forget-me-not-gemini-fort-final-tsukinomizu-project.65603/ is more focused on the futaanri part but still have a decent amount of tentacles too though, and gameplay is more mystery based with very little combat
Nightmare Girls have an almost full English translations over on ULMF
You must be registered to see the links
Haven't played this yet myself, waiting for the translation to be 100% completed (at 99% ATM) to play it personally, so can't speak too much on the details there
Listed order is the order of release, of the games, and for the most part I think that is also the chronological order of the events in the world they are in (they do all take place in the same world, though the stories themselves is only very loosely connected, if at all, so not needed necessarily to play them in chronological order to understand things). As I said not yet played Nightmare girls myself, so can't 100% verify the chronologicality of that one, and forget-me-not is harder to link for sure, but does seem feasible the release order of the original jap version (eng and jap version got 2 different entries in dlsite, and is the only one with its english version posted on dlsite), to match with the ingame cronologicality
