Only Matthews out of that group can cover Gronk. Peppers has no experience marking an All-Pro TE and Neal is not good in coverage. Peppers has excelled in dropping into zones and getting his 6' 7 " frame in the passing lane. Smart, solid football. But Gronk isn't going to be running a route to stand behind Julius. You will need to man up on him to double him.
The problem isn't your 3-3. Its that your 3-3 pulls Matthews out of the pass rush every snap unless you want a player inferior to Hawk/Jones in coverage. That is the conundrum and answers almost all of your questions about why Hawk and Jones still get snaps.