If it’s the first couple of times the pair have bred and a male new to this then you could well find him leaving the cave and the eggs unattended. However, a good older male will sit on the eggs from them being laid until they hatch, ignoring food. Only once they are free swimming will he leave and feed, and usually not going far from the cave. Looking after them for another 5-10 days before either kicking them out or enticing the female in to lay again.
Often, in a community setup the cave design is quite important too. If it's too large and open, other fish can get in (especially if you have other bristlenose) but if it's a nice closed design, generally other community fish won't bother the eggs or newly hatched fry with a male in there. Once they are out and about however, angelfish will happily try to pick them off one by one.
Sounds like you need to decide if you want to breed bristlenose, rear them and sell them on, or if you are happy for them to breed in your tank and nature take its course.
If your gonna look at breeding them then it's worth moving the parents into a breeding tank of their own (note that doing this might stop them breeding though) and you will need at least one ten or fifteen gal (or bigger) tank per batch to grow them on in ( which could be one every month) and you will be looking at around 2-3 months before they are really good saleable size. ( so realistically you will need three further tanks (the bigger the better).
Whilst zucchini and vegetables are good food with good vitamins, I find that nothing fills a bristlenose belly quite like mussel meat - mine all go crazy for it.
