I learnt btb weave before doing btb butterfly, so you don't necessarily need btb butterfly first. Reverse btb weave is way easier than forwards - so when the poi are btb they're going in the same direction as for normal reverse weave.
The way I learnt btb weave was in a series of steps, where I got the hang of each step properly before going on to the next one:
1) practise each hand separately, alternately spinning one circle normally and one on your other side btb
2) practise each hand separately, spinning 2 beats on one side and the other beat on the other side btb. Make sure you can do 2 beats btb as well.
3) now for both hands! spin in split time and practise figures of 8 btb. So each poi goes btb for one beat and comes back straight away.
4) once that's comfortable, it's just a case of forcing one hand to stay btb for a second beat.
Keeping the poi in plane is pretty important cos otherwise it quickly goes pear-shaped and you get whacked. All the separate hands practice should help with this.
I found watching
this video really helpful cos when I got outside, I knew what I was meant to be aiming for and I could kind of feel it when I started getting the rhythm right.
Good luck
