those are questions for a real met.. but i'll try to answer them.
i can't describe the ridge to the north and it's relation to the other features other than to say it's THERE. its strength and configuration is more related to the longwave pattern.. right now we're transitioning back to NAO positive.. a flatter pattern.. and the ridge is sort of unbunching and pancaking across the atlantic. the upper features are responding to this by becoming progressive underneath.. you did note the tandem movement of the upper lows and isabel. their presence requires there to be an upper high between, in this case isabel's outflow. all of these systems are at outflow level.. 200-300mb... the ridge is more of a 500mb feature. bastardi if i remember uses the 400mb contour for the hurricane's path. anyhow, about the slingshot thing.. the systems are all moving together.. but they can apply the squeeze to one another. isabel is strong though.. and can push back. eyewall contraction cycles and fabians wake might weaken it quite a bit (remember georges going from borderline cat5 to high cat2 as it approached the virgin islands?).. but very unlikely to kill it outright.. even if it does weaken it will stay further south and go with a shallower flow. i probably killed the answer i was trying to give in all of that explanation.. but hopefully you can sort it out of my attempts to explain something i'm utterly fascinated by but am not an official source of understanding on.
take it easy.
HF 0358z10september