Unfortunately, if they were low altitude, only four crew would have a chance at survival.
Pilot, co-pilot, EWO and gunner seats all eject upward. Downstairs Navigator and Radar Navigator seats eject downward. Unless the pilots could zoom climb the jet to get a positive velocity vector for the two Navigator seats, then those two crew would not likely survive a low altitude ejection. Those would the the six crew seats.
There are additionally two jumpseats, one upstairs and one downstairs, that aren’t ejection seats. Anyone in those seats wears a backpack parachute. Both jumpseaters have to manually bail out of the discarded downstairs lower fuselage hatches once the navigators eject. If the upstairs jumpseater can’t get aft and down the ladder to downstairs, or if the navigators don’t eject, the jumpseaters can’t bailout either. For this reason, the jumpseats are not normally used for anything, unless for specific checkride requirements, where a regular seat cannot be utilized; or in this case, for flight test purposes. This came out of a 16 October 1984 crash of B-52G 57-6479 out of Fairchild AFB, WA, which was on a night, low level training flight about 15 miles northeast of Kayenta. AZ on the Navajo Indian reservation. During a ridge crossing, the jet clipped the ridge and rolled out of control. All six crew ejected (gunner killed), but the sole upstairs jumpseat occupant, a senior Colonel who was the deputy commander for operations of the Bomb Wing, had no time to unbuckle, much less time or altitude to get aft and downstairs to the bailout hole.