Silicone liners aren’t essential but a lot of people use them. If not too mucky we save tin foil trays from takeaways and freezer meals etc and reuse these for some things in the AF. Not exactly necessary but saves a bit of washing up.
One important accessory (vital IMO) is a meat thermometer...
Can definitely do a Sunday roast in a dual AF if there are 2-4 of you but beyond that, it might be tricky. As I said above, a joint in one half and roast pots in the other works a treat though we still use the hob for steaming/boiling veg. I'm not a fan of baked everything.
We have a Ninja Dual 9.5L. I can't comment on whether it's suitabe for a family of 4. There are 2 in our household and it's more than adequate. Depends a lot on what you're cooking. If you're just reheating stuff or cooking sausages and bacon, or burgers etc, there's no problem at all. We can...