If I wanted to do this, I would have the rented points transferred into my account. That way I would have control over the reservation (rather than the original owner of the points). I could make the additional reservation at the same time I made mine, I could add requests later if need be, or make changes with MS and just generally deal with all the things that may come up when organizing a multi-family trip.
Most members seem to prefer to deal with other members - for the owner who had the points to begin with, it's a final transaction wth little or no hassle involved.
I'd also try to get points from my home resort and if possible, from the same use year (or at least one close to it). That would give me the maximum flexibility for making and cancelling reservations and also be the easiest to track.
Best wishes -