As mentioned before, it's IST-LHR where there is a ban imposed on laptops in hand luggage, not OSL-LHR. Was it the check-in at IST but told you you could take it as hand luggage on IST-LHR but not on LHR-OSL? I'm a little surprised because they should know at IST that it's an IST issue rather than LHR/OSL issue. You definitely can take it on board for LHR-OSL, so there appears to have been some kind of a confusion there between "can" and "can't".
As for the children, BA is not obliged to seat the family together, however, one adult must be seated in a seat adjacent to the child. It appears that the requirement was met, but for some reason they couldn't seat everyone together.
Saying that, you mentioned you checked in at the CE desk due to status. Were there issues with advance seat assignment on the basis of your status?
Last edited by LTN Phobia; Dec 14, 2017 at 3:34 pm