I'm also running with an awful party composition
I am not super tactically minded and don't have a lot of 5e experience, so I'm not good at exploiting weaknesses or anything like that.
Sounds like you two should be having trouble. The balance is good, besides some silly AOE issues. What's needed is an easy setting, which there will be of course.
Most of my big combats end by the skin of my teeth after having pulled out every spell and ability I have.
As it should be, in my opinion.
