As Janie says, the centre is the safest place. But it's not always possible. We have two that won't fit side-by-side, so we have to have one on each side. And if it's too hard to get the child in and out then it wouldn't work either. But if you can, you should go for the middle.

As for visibility, believe me, wherever they are they will see well!

BTW, how heavy is your 1yo? You should keep them rear-facing for as long as possible, it's MUCH safter. Most car seats allow them to be rear-facing until 12 kgs.