Mark,
Yes, I see the shared bunker situation quite often and Tom Paul is correct, they were often utilized on some of the early Ross courses, at least in North Carolina. I have also seen Perry Maxwell use the shared bunker feature at Old Town Club, probably just a replicated design feature from The Old Course which he so admired.
In every instance, whether the bunker was a shared feature on parallel holes running in the same direction or parallel holes running in different directions, the land used was open and barren. Most always, however, the parallel holes were maintained as one big large fairway and the bunker placement coincided with landforms running along the center of play. In this instance, don't move the shared bunker away from its natural landform. This would compromise the two holes. Instead, move the tees to bring these landforms back into play.
I've also seen them used strategically in this manner...... Placing shared bunkers between two fairways where the preferred safe route to the hole required you to play along the outside lines of the parallel holes away from the inner bunkers. This being the case, the subsequent trees which have since divided these holes and camouflaged these bunkers actually serve little safety purpose since most golfers actually played out wide and away and not along the riskier inside line.
Many shared bunkers though, I have noticed, did not even strategically come into play even by classical standards of length. Some, I've noticed, were 100 yards off the tee on one hole moving North and the same shared bunker would be 270 yards from the tee on the adjacent hole moving South. I think at times shared bunkers were merely used to psycologically separate and establish the corridors of play visually. In this sence, it is not necessary to move back the tees or the bunker.
Hope all is well.
Dunlop