i have 1 4x4x7 and 1 3x3x6 tent i have a 6 inch exhaust fans in both tents , i am wondering if it would be possible to have maybe 1 8 inch exhaust fan with a 3 way splitter with a hose going to each tent with 1 hose blowing the air to the outside
Yeah absolutely, that's pretty close to how mine are setup.
Just set a big can filter on the floor (or hang it or w/e) between the tents, stick an 8" fan on top, Y pipe on the fan, and flex duct to either tent. Airflow is blowing into the tents so there's positive pressure, no need for additional exhaust fans for each tent.
Since you already have 6" fans I'd recommend repurposing one of them for a room exhaust rather than splitting off the new fan for the tents.