Mindzeye82 , welcome to flyertalk, I do hope you are able to stay.

In fact you are correct about there being complexities here - as the reservations are overlapping, but with slightly different end dates and Marriott's policy has change as a result, there is more here: FAQ : Points and stay credits for multiple rooms (new policy effective 30 Aug 2023) . The risk is that the 5 night points reservation will end first and will "block" a subsequent reservation from posting with overlapping nights, if it was going to credit to your own Marriott account, which may cost you your cash earning.

In your case I would do two things:
1. Make sure that the points reservation is set up as a "gift" in another family member's name, and if possible remove your Marriott number from this reservation (so that it doesn't accidentally post before the six night stay)
2. Put all of your incidental spend, if any, onto your cash room, so that you get the points (along with any elite bonus) posted there, after the six nights. Due to the new policy earning, requiring room dates line up, any incidentals put against the points room can't be credited to your account.

In the past you could have combined the rooms onto one bill and it would have probably worked out ok, in this case it probably wouldn't (and since the second booking is a points booking, it doesn't matter as there would be zero earning anyway), I have a feeling that if you did try and combine them at the hotel it would probably work out, but may need some manual intervention later on, and agent back-and-forth, so you may as well reduce the chance through step #1.