Actually you can do one reservation online using some borrowed points, and then attempt to do a second reservation, and if you cannot get to the point of availability in that second reservation, you can cancel the first one and have borrowed points returned to the original use year.
When doing any successful reservation, you will get to the last page that confirms it. That page also gives you an option to completely cancel the reservation you just made, and all points go back to their original location (including borrowed points are returned to original use year).
The key to making two reservations is to get to that last page for the first one and not close or leave that page in the window you are in. Instead, open a new window on your computer, go to the
DVC site and then start the second reservation that you want, if you get to the availability page showing the reservation is available, you just continue to complete that second reservation -- and it will show points to use on the basis that first reservation is already confirmed.
If in attempting the second reservation, you cannot get to the availability page because the rooms are filled, you can then go back to the original window and cancel the first reservation, and points will be returned to your account as if no reservation had been made.