No, the CEP numbers quote in the specification are under the most optimistic conditions.
The antenna on the SAM-M8Q will also detune in the presence of the human-body.
It might be possible to buy SAM-M8Q's capable of outputting raw-measurements and use RTKLIB (or whatever), but such parts would likely be priced with a significant premium.
For indoor you're going to need to use other methods, beaconing, wifi heat mapping, INS/DR
You should perhaps seek out consultants with actual experience in this area, or purchase solutions from companies with pre-engineered solutions. Seem to recall a German company that was tracking football players, and people with shopping carts inside a super-market.