The official answer I got from Marriott email respond is based on the staying guest status. And I had check-in as Platinum and got Platinum benefits like free breakfast / lounge / upgrade on a cert that book under a Silver status account before. But I did contact the hotel in advance. On the other hands, friends/family members that have no status but using my certs (Platinum status) had got Platinum benefits so far. We didn't contact the hotel in advance. So, my guess is that if you do nothing, the hotel will apply benefits of the certs owner as that is Marriott Rewards number attached to the reservation...but YMMV
When you are doing option 2 and changing the reservation name, are the night credits still showing up in your account or are they showing in the family member's account?