One thing that seems odd to me about this situation is that I don't think I would expect/want someone to help me wash dishes, whether they were a guest or a visiting family member (who didn't live in the house). Kind of like what fountainof said--it would be like going to someone else's house and doing a load of laundry or vacuuming. If you're going over there specifically to help someone out with these chores, obviously no problem; or if the family member/guest is staying at the house for several days, I think it would be fine to have them pitch in with chores.
But some things just seem too involved for someone who is just "passing through," like standing at a sink washing dishes, which could take a rather long time as generally only one person can wash at a time, even if a second person is drying and putting away. Taking plates and dishes back into the kitchen after the meal, or setting the table before the meal, is much less involved and seems fine to me to ask of a family member or frequent guest.