I disagree that an engineer should be called.

Framing/headering in an opening is pretty standard carpentry. A licensed contractor should know how to do it, and they are not required in most cases to have an engineer design it for them.

I really hate to pull the engineer card just for CYA, especially when it is so "basic" as framing in an opening where a joist needs to be cut.

If there are joists that need a ledger board or hangers installed, I wouldn't expect to need to call for an engineer either.

Could it be done wrong? Sure. But we don't call for a mechanical engineer to design a repair when we find some loose ducts. We reply on licensed contractors to do the right thing - and a good part of them do.
JF