Your right, they will keep spawning. So yeah, the females as well as the males seem to wear out a little with all the spawnings and no time for regeneration.
Splitting them up is definitely good to get them back into shape.
However, splitting them up might stop the spawning rythm and even after a reunion you might have to wait for new spawns to happen again. I wouldn't want to risk that right now. A viable spawn might just be 2 weeks from today.
In your current position, I would add more structure (wood, caves, slate, plants etc.) so the male won't chase the female that much (maybe create 2 feeding places -> no fights over food) and let them keep going at it for now until you receive at least one viable spawn with fry. Split them up after that for regeneration and to not be overloaded with fry in an instant.
If you have any more BNs than the breeding pair in that tank, try removing them, males can be harsh.
BNs usually spawn everywhere, but maybe you can help your dad with a smaller/narrower cave? Sometimes a very small cave is best and preferred. Even if you think it would be way too small, give it a try, the male will chose the right one by himself.
As was pointed out before, having the opening of the cave going upwards, so eggs would not roll out by themselves, can be a good idea.
Edit: Eric was faster
. Enjoy!!!
But don't worry, I won't - it's easier, and much kinder to the fish, to simply separate them. 
I'm kicking myself at the moment, as just went to the LFS, a pair of adult BNs (normal morph) came in on Wednesday and I was going to go and see what they had in pleco wise, but didn't. They spawned and then the female was sold, sure my male would have taken up the opportunity, and possibly got it right. Although two females is too way much in terms of fry production rates.
The cutest pleco picture ever, My pair of ABNS kissing and making up.
