The spider matriarch is pretty easy, you can kill a lot of the little spiders by shoving them off the cliff, and you can also burn the webs. If you burn the webs it means that the spiders can't just walk up to you.
I had no trouble with this fight following the ideas I just wrote down with two different comps. First I was Cleric, Astarion, Gale and Wyll; second was, ranger, Astarion, Gale and Lae'zel.
Astarion is the MVP, he is seriously the best party member you can recruit
, put him on thief specialisation and he gets double Bonus Actions, it's the BEST!
Use the Dancing Lights Evocation Cantrip as well, it'll help get better hit on the matriarch too. There is also Alchemist's Fire that you can pick up from the Doctor's Laboratory too.
