Tough Bathroom remodel in old house

[#22]

Greetings all!

Tore out an extremely poorly done bathroom in a house we're managing today. It's an older house, with a few additions and remodels throughout its lifespan. As one would expect, we ran into some issues and are working on cleaning them up. The knuckleheads before us, who did the awful remodel simply threw their trash into the crawl as they did the work.... Some examples of the previous remodel include: having a light switch inside of the shower surround and a shower surround made out of sheet goods not made for water exposure.....sigh.......

We'll be going back with a solid 1 piece fiberglass enclosure like we usually do and ride on down the road and sheeting it with advantech.

The issue we snagged is that the floor joists are all 2x6 and appear to be possibly overspanned. A few are pretty trashed and will require us to tear up the ajoining bedroom to get at repairing the situation fully. I pray that as we peel up the next room's floor 100% that we aren't forced to continue into the next/adjoining room. The 2x6's I'll add, were poorly braced by a few 2x4s.....

Our plan for now will involve doubling up the 2x6s or decreasing the centers to gain a little more strength. I'm also figuring on adding some 6x6's as supports to help carry the load.

I'm trying to figure out the best way to do the following:
Run the new 6x6s. Are we better off doubling a lot of them or decreasing their centers?
Support posts - are we good with setting solid 4x8x16 blocks on the ground and bracing up off them or should we dig it up a little and pour a small footing to brace off of? I apologize for not having any pictures of this.

Thank you so kindly for any advice and wisdom - I appreciate it!