Is this possible? There would be two separate ressies - ours (DVC) and sister's (non DVC.) Can we link them to try and get rooms one another or would we be forced to try to do that at check in?
Linking is the joining of two reservations held by the same person. It is done to ensure that the member (guest) remains in the same room through the dates of both reservations. You can not link your reservations. You can not link reservations that are not made through Member Services.
You can make a request on the DVC reservation that you be close to the family of the non-DVC reservation, and again ask at the desk on check in.
If you have 8 or more guests over the age of 3 in total on both reservations, it can be set up as a Grand Gathering. It's not easy to do with DVC and non-DVC reservations, but it is possible. In that case, the rooms should be assigned near each other automatically.
Otherwise, they can put a notation on the reservations that they should be near each other.