Try and get a row of 4 together, even if it means paying an additional fee for the baby to have a seat. You'll be glad of the space. If your 1 year old likes their car seat, see if it's possible to take it on the plane. Some fit in the seats, some don't. But we flew with dd when she was 13 months, there is no way she would have sat on our laps for the whole flight, but happily sat in her car seat for an hour or so, then we'd get her out for an hour.
Get a kindle, load it up with cocomelon, peppa pig etc with some Bluetooth headphones. Even if it's only used in short bursts, my 3 year old loves hers on long journeys.
Check your terminal, but some have a small play area for little ones which is handy for wearing them out.
When boarding starts, one of you goes ahead with the bags. Set up the seats, gets the kindle, drinks, comfort toys, nappies, wipes all stored in the seat backs. Then the other one waits in the gate walking the kids round letting them have as along as they can. It can often take 40 mins to board a plane. If you are first on with the kids it's an extra 40 mins they are on the plane.
All the snacks.
Change of clothes in your hand luggage for everyone (a couple for the baby) just in case. And a couple of plastic bags for dirty clothes.
A few small 'new toys'. I've seen one on Instagram someone bought a roll of masking tape and stuck little strips on the back of the seat for their baby to peel off. It seemed to keep them entertained, wasn't messy or disruptive for others.