I've done this for 5 people - mixed class F and J, had to phone but dead easy to sort out - BAEC are used to it - and no fee to pay, even when I phoned a few days later to move the dates. You end up with one PNR per 241 (in my case 3 PNRs).
Only downside, as already mentioned, it that any 'warm glow' of your own status only applies to the PNR for the person with status. So I can get the upper deck seats in J for me and SWMBO - but the children will have to take pot luck on the main deck (I am not paying £240 for them to sit upstairs

).