With a nervous flyer i would def choose the middle seats - whilst not the best, they are sat together with a small screen separating you. Its very easy to have a conversation. On the 747 i'd chose the 5e/f - its closer to the galley but 4e/f is slap bang in the middle so feels more exposed.

I like the front row of the 747 but find it a little claustrophobic and if people are using the wardrobe it can be a bit irritating. WE generally these days choose row 2, its close enough together but far enough apart (if that makes sense)

On 777, the rows are offset so choose e/f pairs again if you want to sit together - there are no bad seats really. To me, the 777 has more personal space than the 747