NovaScotianNorse

The option isn't there for any combination that includes Shadowheart, and Laezel x Karlach isn't in the base game either. Those are the ones that interest me, so I'll have to wait for a mod. You can romance Shadowheart and the druid at the same time. Shadowheart is up for poly romances with certain characters. Astarion is as well. The druid will accept a poly romance, if it's with either Shadowheart or Astarion. There's another character you can replace the druid with, as long as the third character is Shadowheart or Astarion. You can't have those two in a romance together, and Shadowheart will not accept a romance that includes Lae'zel.

There is a mod that adds Drizzt's equipment to the game, including a statue of Guenhwyvar that equips into the helmet slot, and summons a black panther familiar, using the tiger stats from 5e. At the moment, I think that's the closest that's available.