I think the ISS has 3 docking hatches for either Soyuz or Progress.
Two are needed only for replacing one crew by another (the latest Soyuz must dock before the first Soyuz can leave).
Your scenario would need all three hatches for the Soyuz vehicles and hardly any time (and space) for the Progress. The Progress must be able to stay months docked as it is gradually emptied or filled up and there's fuel for the ISS orbit corrections.
And another problem: each Soyuz vehicle needs two cosmonauts that have trained to pilot the Soyuz. Only one cosmonaut out of three would be a true scientist, specialized in systems aoard the ISS rather than aboard the Soyuz.
So, with 2 Soyuz vehicles for permanent occupancy, only 2 cosmonauts would be useful aboard the ISS.

Raoul