We should emphasise that littlevoices has outlined the correct solution for you. Make the points reservation as a gift in the other person's name and thereby remove your Bonvoy account number. I've never gifted anything in this way but I believe that you have to call Marriott to do gift reservations which is a pain but it is the correct way to use points for a stay that is not your own whether you are also staying in the hotel or not. This way, your family members will check in to a reservation in their name and check out the day before you and the reservation will not be associated with your Bonvoy account for the purposes of EQN accrual or the welcome gift points neither of which you are eligible for as you have your own overlapping reservation. You are correct to approach this scenario with trepidation because unless you fix it like this in advance, there is a risk the points stay will post first with 5 EQNs and welcome gift points and your 6-night paid-for reservation will not post according to what you want.

In general, overlapping reservations must begin and end on the same dates to post correctly (one lot of EQNs + one welcome gift points + points for up to three room rates and charges). You'll get used to not-particularly-customer-friendly rules in Bonvoy that appear to be driven by IT quirks that cannot be fixed. Very much the IT tail wagging the Bonvoy dog. You came to the right place to get understanding. Welcome to Flyertalk.