Not sure where to post this question. But I normally only book *A.

Is there an online tool or some other trick to take care of this problem?

For example, the 5804 family needs 4 tickets. However there is only 2 ultra low discount tickets left. How can one book in one go; 2 pax in the ultra low discount booking class the remaining 2 pax in next available booking class.

I have some concerns about make two purchases, because seats for the 2:e booking could get taken by someone else. Or even worth the travel insurance may not be valid for the pax that are not booked together with s5804?

The goal is to get the cheapest deal, and ringing up a travel agency is often a worse deal due to handling fees.
Be grateful for suggestion.

THX