Alas, I have no experience with Avast, EMET or Sandboxie.
And I have no Win7 VM to test any of this.
So, we'll need to wait for a tech expert.
I will offer this friendly observation: At some point, loading up this old hardware (and old OS) with a ton of "security" apps and configurations might backfire in terms of degraded performance or worse (unbootable system).
And this friendly reminder: no one program/application OR conglomeration of programs will provide 100% protection for an outdated system.
The weakest link in the system is the user.
(This is not directed at you personally and no offense is intended - it's just the way things are.)
I'm afraid that you're fighting an uphill battle, and investing a LOT of time to salvage this system.
It may be time to resign yourself to the need to move on.
I understand & accept that you (and others) may well disagree.
Respectfully submitted