I think that Tom could simply say to the husband - "Okay, I'll be about *X time* with your wife, so you're fine to go back to the waiting room. Policy is that we only have patients in the therapy area so they're able to fully concentrate on instructions."
If the husband demurs, then Tom needs to tell him (not ask) "Yes, I understand, but patients here need to concentrate, so we don't allow other people in the treatment area."
And if there is still a problem: "It makes other patients feel quite self-conscious if there are people here aside from actual therapists and patients. You need to wait in the designated area. Thank you." Then actually walk him out.
If none of this works, then Tom needs to go up the chain of command. Obviously, this gentleman feels he's assisting, when he's really doing the opposite! Polite but firm, citing policy, and explaining why this policy is in place should sort it.