I think this is somewhat a rare case. We are allowed to invite friends and family members to join an Area 51 proposal and contribute to the proposal. We can also share a link to Social media plat forms and send a question who can answer. I have done it a couple of times. So, this seems no problem till here.
When one of our friends or a family member joins the site and answers, we should be careful while voting to them as it may look like serial voting and sock puppetry should be avoided in most of the cases. But the thing I'm concerned about is reviews.
I think if two or three family members (living under the same roof) are members of the site, it is a common thing to come across each other posts. Similarly, it happens in the review queue too. When one family member suggests an edit, others might see it in review queue if they have privileges. Same for other review queues too. If they act in favor of the question (like approving an edit or leaving open in the queue), is it considered a part of Sock Puppetry? Because we never know if it is the same person who operates the accounts and vice versa.
Should we review the item just like we do for other users or let the other users review it? If it is left to other reviewers, we don't know what other users think of it and this may effect on the closure or sometimes existence of the post too. So, what is the best way to deal with them?