Hi of to Eygpt in 8 weeks, four of us traveling 2 adults & 2 children aged 7 & 9. Normally I would pre book my seating but friends we travel with never do and always get sat together, but I keep worrying now and I am panicing that we won't all be sat together on the plane (is it likely to happen

). Do you guys pre book seats or would you rather put that money towards your holiday spends?
Also we only have a 15 kg luggage allowance each, which gives us 60 kg between the four of us, I will only be taking 3 cases, can you spread the allowance over 3 cases? ( for example 1 case weighing 19kg and 2 of 17 kg), or will i be charged for going over my weights for each cases?.
We will be traveling with Thomas Cook thought I should mention that as I know all airlines are different!!
Thanks in advance for your helpful replies.
Vickie