Hey everyone, my friend and I are in the middle of a BG1 playthrough, and we were foolish enough to resurrect the priest of tymora's son before we got poisoned by malek and lothander. Unfortunately that turned all the priestesses of umbralee hostile to us, so we murdered them all. But now we're stuck with 10 days to live and no way to get to the high priestess of umbralee. Any clues as to what we can do to save the playthrough?

You should try asking on Reddit, the core players are mostly there.

Have you tried using cheats to summon them? Would you be able to go back to an old save and charm someone at the temple?

How would I do that?

You didn't specify what version of the game you're using, but as for the original:
You have to open the baldur.ini file in your Baldur's Gate folder and add the line Cheats=1 under [Game Options]. Then in the game you need to press Ctrl+Tab and write in the console and then press Enter:
CLUAConsole:CreateCreature("Jalant") - this will summon the high priestess Jalantha Mystmir (the other priestesses are not required for that quest)
or
CLUAConsole:CreateItem("SCRLJALA") - this will summon the geas removal scroll into your inventory.