She looks a nice boat, and I understand what people are saying about a bench seat, but I took mine out after the first day of use!
I found the kids on their own had a habit of sliding, and with the wife with them far to much weight at the back for a small boat (4.7).
My advice is think about how you're going to use a boat, where and for how long as this will change the configuration you need.
A 2 year old will need direct control so a seat to do this could be a double jockey, or in my first 4m we had a barrel that the little one sat on in the bow - and loved it, whilst the wife was tube sitting alongside. This was great on a flat day, at slow speeds whilst Aaron was small, but he soon out grew that position and we had to change boats!
The daughter (from around 8) was happy to stand at the seats and preferred it to sitting, this is fine for short hops but not good for long passages so something to think about.
My current configuration is 2 side by side jockey seats with a console seat in front. This would work for you I suspect, so long as the sea isn't huge
Having the 6 year old behind you on a jockey works well (it does for me) and I think would work on the Tornado (which I think are great boats) which leaves the wife and kids at the rear which again will be fine so long as there isn't too much weight there.
The good news is the 4.5 is a nice size to learn the craft in, this one will give you a good ride with the option of taking out the bench seat and adding in another jockey seat if the bench doesn't work, maybe a side by side pair if you're lucky and a console seat in front perhaps (although others hate these as bad as marmite they are fine if used correctly).
Knowing that you'll probably be launching at Appledore you'll have the whole estuary to play on and get used to the config before going too far away from land.
We moved from a 4.1 to a 4.7 to a 5.5 as we kept growing out of the boats as the kids grew. That's partly my fault as they are both happy at speed, wave jumping, longer passages etc and this just isn't safe in a small boat with a configuration not set up for the use. Had we stayed picnicking at Appledore or within the Sound the 4.1 would have remained great.
So in short think about your use now, your intended use and how the family will grow.
I will always suggest get the largest you can store, tow, manage, afford as you'll soon grow out of boats if you're not careful, a 4m for your use sounds too small to me. If this one is as good and as tidy as the picture suggests it could be a good first buy.