Most seats are simply held in by 4 bolts and whatever electrical, I rarely disconnect the battery unless I'm working directly on something like the main electrical, you can if you want, some people and manuals say to do it for almost everything, although I havent heard anyone say to do it before checking the oil...yet. I suppose if they tell you, then they arent liable if you short something and for some reason the fuse doesnt blow.
Most back seats just pop in, I think these ones pop in/out when moving the seatbacks, but need to be unbolted before you can remove them, I think I remember seeing bolts for them.
Older seats had to have the tracks lined up before you put them in or they would be crooked, which makes it very awkward and uncomfortable to sit in, especially if its the drivers seat lol. There is nothing complicated about changing a seat, except for seized bolts sometimes. If the bottoms are rusted, its a good idea to paint them before putting them in, it looks awful having a rusty seat bottom next to a nice clean carpet.
That must have been quite the expense, unless they are used seats.