Stringer(s) to carry load of floor joists where chimney breast removed

I'm removing a chimney breast which has 2off 2"x7" ceiling/floor joists sitting on it. (yes I issued patry wall notice & notified BC etc). I understand from the building control guy that I can put a stringer(s) across between the 2 joists beyond to carry the weight of the two joists which were sitting on the chimney breast and then have 2 short lengths of 2"x7" Joist from the stringer to holes in the newly exposed wall. I understand that for roofing work you have 2 stringers side by side for every joist removed, does that mean I would need 4off 2"x7"stringers side by side for 2off 2"x7" joists?

 

Umm yes, sorry stringer should read trimmer, I can't figure out a way to edit the original post unfortunately