No, I don't think your priceing is correct. Firstly the UUA pricing doesn't use the RFS prices, but the standard avios pricing, which I think is the 3rd option in the list. Secondly, because you're looking at a one way, you're getting the one way KUL-LHR taxes and fees, but your actual booking is a return, so will be taxed differently.

To get the correct amount you need to do two dummy bookings, first do a dummy UuA booking, in WTP, upgrading the inbound. Ignore the total cash amount (as this depends on the WTP fare at the time, which you've already paid), but look at the avios and taxes amount. The avios amount is 42000pp, this is what you'll have to pay. (see first image).



Then do a dummy CASH booking in WTP, scroll down and look at the fees (again ignore the total cost), see second image.



Here you see the taxes and fees for the WTP booking total £584.59. Subtract that from the taxes and fees amount on the first dummy booking to get the cash amount to upgrade. So to upgrade you'll pay 758.29 - 584.59 = £173.70pp

So the total upgrade cost will be 42,000 avios + £173.70 per person. For two of you double it.



As for your other questions, you can't upgrade BA Holiday bookings online, even for a cash upgrade, you have to call. So wait for the seats to become available (if they ever do, no guarantee), and call up ASAP if/when they do.

And as the other comments say, you should get the avios and TPs for your original cabin (ie WTP), though sometimes BA's legendary IT will giveth you the CW points, and sometimes it will taketh away, and give you nothing, in which case you'd have to call to correct it.