You probably find your answers in
Upgrade questions - two people on one pnr
Upgrade SYD-SFO/LAX: One PNR or Two?
Upgrade clearance policy for 2 travellers

potential downsides are discussed in
Upgrading kerfuffle -- how could I have avoided this?

Large number of hits if one searches "split PNR"

Note- realize the above are upgrades situations and OP is looking for awards tickets, but believe there are many parallels and there is some discussion of awards in the threads
Questions: waitlisted for F award NRT-BKK-NRT; when to buy standard award is a bit closer