How efficient would farming be with 3 people rifting and one person doing bounties. Basically you take turns on who does bounties while rifting. Everyone gets the rewards for both then.
You mean within one game?
Bounties are generally done on Normal and Rifts are done on the highest level that the group can do within 10-15 minutes. So there's a clash of difficulty setting there. If one person was doing Torment 1 Bounties while the other 3 were doing Rifts, I don't see this as being all that fruitful for the one person doing the Bounties. At high levels you want to be in the Rifts for the 100% bonus otherwise you are just wasting time gathering gold/exp (the rate of Cache would be too low to be worth a damn).
Most efficient way to get Caches: Split bounties on Normal on a single Act (4 people do one Act if you are all looking for a particular item).
Most efficient way to get Legendaries (non set items): RIF then gamble for them
Most efficient way to get Sets: Rifts at the highest level you can complete in reasonable time.
Most efficient way to get Blood Shards and Forgotten Souls: RIF
Most efficient way to get Gold and EXP: No stop in between RIFs (if you have to wait too long in between RIFs then it's not efficient) or Hell Rift 2 Act 4 Bounty or Ghom if your DPS is outrageous like some WDs.