A vital point however, if allowing anybody else to handle the main flight controls.
Some clear variation on "I have control" / "You have control". If you are letting them handle the controls - do so consciously and deliberately and they should accept that. If you take control back, the same applies.
Two people handling the controls at once is seldom a recipe for happiness, except in very particular circumstances. A passenger handling the yoke only whilst the pilot does everything else is one such circumstance, a student or instructor following through is another.
Whatever circumstance however, absolute clarity about who is doing what (as well as who is in charge) is vital.
G