Leeds to London for family of four (book at least 7 days in advance) £105 Return @ LNER

Just back from London, to Scotland, on LNER with my kids. Train was delayed and staff advised to claim through the LNER delay repay scheme. Was only delayed by an hour but it was easy to claim so gave it a shot. Was surprised to get an email back the same day refunding the entire fare. Was impressed with that so make sure you put a claim in if you have a delay more than 30 minutes.

Family and friends railcard, use £10 worth of Tesco vouchers to get one, save you 1/3 off the fare

£105 for a family, but £109 for one person.. I hate this. :/

Trains are okay (assuming you can all get seats), but if you're going from a major city to London then National Express, Megabus or Flixbus would likely be considerably cheaper booked in advance - I've taken my two kids from Nottingham for something like £15 return for all three of us a few years back. (edited)

Does anybody know if you can purchase a family ticket and just travel with two adults?

T&C's seem to suggest that not travelling as a group invalidates your ticket and will result in the passengers having to purchase the correct tickets on the day, but I just wanted to check.