welcome to FT
the middle seats in row 79 are pretty bad, i'd imagine. I haven't sat there, but there's an extended space between rows 79 and 80, and passengers can often use that space to walk through from one side to the other during the flight. when they do that, some of them may grab the back of your headrest as a makeshift handrail...

you probably chose those seats as they're the only ones available for you right now. my suggestion is to go back once online check in opens up, and choose better seats.

personally, even if travelling with a group of 3 (and even if one of them was a child), i'd chose a window and aisle seat on either side of the plane, and then an aisle seat closest to the reserved seats (so, A, C, D or G, H, K).

if for whatever reason, you MUST be seated together, choose D, F, G on any of the other rows. If you're lucky, E will be left empty. If there is someone sitting in E, then offer to swap seats with whoever is sitting in D. they'll surely prefer an aisle to being stuck in the middle of a group...

hope this makes sense