Oh dear.
It is perfectly normal yes, but it's how it develops that will make a difference.
I have the humpmeister here (Bugsy) who has returned for bonding with his two wives. The last few times we tried to bond him (the last time with them too) was about 2 months ago and he wouldn't stop the humping.
So he was sent to his new home to live side by side as we felt that he'd never be bonded and therefore never be rehomed (as this was the umpteenth try).
He came back yesterday and he was a totally different rabbit, for about an hour, and then he started again. It got progressively worse and I've been up all night with them, having to stop every few minutes, but about 5am it subsided and all is calm again for now.
Not knowing Gert's full history and why she is humping, it's hard to second guess how it's going to go, but she may just need to assert herself and when BJ has allowed her to be in charge she'll decide she doesn't need to do it any more.
Of course if it's sexual, then it may not subside quite so quickly.
If they don't settle Jill, I'd put them in the carrier and leave them in it for 10 minutes or so, maybe even longer and if necessary take them for a drive as they would prefer to cling to each other than be scared traveling. I suspect it could possibly have the desired effect on BJ.
With him having been the 'dominant' or at least 'top' bun in the previous bond, this is all a bit strange for him so it will take a while to settle down I'm sure, but a change in the heirachy and behaviour after 24-48 hours is so very normal so don't give up the faith.