Hi there - yes, for this to happen automatically and/or via the website, you'd all need to be on the same PNR. If your husband (or indeed you, or your children) were Gold card holders, you could phone up and get BA to virtually link your bookings together and allocate seats next to each other. But this is a manual, back-office process, and you wouldn't be able to do it yourself via the website.

You could of course all pay for seat allocations, but that may be a rather expensive option. Alternatively, it may be possible to find seats together during check-in, or by asking airport staff or cabin crew if some other passengers may be willing to move to accommodate you all.

If none of those are possible, your solution will be to give your husband your boarding pass, so he can look after the kids for 13 hours, while you fly in splendid peace and isolation!