Re. top bars, start harvesting.
One of the advantages of crush & strain is you don't need a big centrifugal extractor to harvest (& the subsequent clean up). so you can harvest in stages even taking a bar or two of single source honey just after each flow.
You could reinforce national 5 with some frames of brood from a stronger hive or even swap it's position with a stronger hive.
I would double check there are no disease issues first though. A lack lustre colony, when all around are thriving, could be the onset of something nasty.
Although it's probably just an inferior or failing queen.no smilies
I hope if the weather plays ball on Tuesday my day off I can have a good look at what is going on and see if I can see the queen,
and move a couple of frames of brood in there perhaps they just need a bit of a kick start
and might have a go at squeezing out some honey from a few top bars
I am impressed with the top bars they seem happier better behaved bees :Dno smilies