I just did this for the 3 of us.

I used elite upgrades on outbound, miles on return.

When I upgraded return a month before flight, I had to take all miles out of 1 account since they could not split the record. I had wanted to take the miles out of each person's account.

For the outbound, there were 3 seats available for upgrade at my wimdow. They then split the record and I used 2 complimentary upgrades and upgraded the 3rd with miles.