Hi Jack, one idea is to build a sweep that sort of arcs through that whole area, like the attached bike_sweep.zip, then hack off the part of the sweep you don't want to keep, either by doing a boolean with the other part, and then filleting the in-between, or possibly trimming with a profile curve and then doing a blend between some open area between the 2.

That might give you an idea, I'll see if I can come up with some more for you later but it won't be until tomorrow.

But generally branching structures can be really hard to build directly, it is usually better to sort of build more simple broader things that extend beyond and then trim those back.

- Michael