Yep, they're all hybrids so they will probably be fine with the higher perch (none of them are meat birds - all bred for laying). I think they're a bit confused because they've said Light Sussex (a pure breed) is the same as Sussex Star (which is actually a Light Sussex/Rhode Island Red hybrid) and they say Cream Legbar (a pure breed) is the same as Skyline (which has Cream Legbar in it but is a hybrid). But the pictures look pretty - I would go and visit to be absolutely sure. They don't mention whether they actually breed them there (that I could see) so ask to see the parent stock and go with your gut instinct. I know there are some hybrid breeders in Kent that have a bad reputation but I don't know who they are, I'm afraid. Just be sure that you're comfortable with how they look after their birds - you want to be sure you have healthy birds from the start.
The only real difference, as I understand it, between hybrids and pure breeds is that pure breeds breed true i.e. the offspring will have the same appearance and characteristics as the parents. But hybrids have been developed to be particularly good in something specific - whether it be egg laying or meat (or fighting but that's a different discussion!). The egg layers tend to be fab for two or three years and then tail off quite fast. Commercial egg producers keep their birds for 18 months and then cull or sell on. So just be prepared that in a couple of years, you need to get more birds in and consider what you'll do with the older birds. I believe hybrids have a lower life expectancy so that, in a way, helps - but they can have more health problems too.
Three or four will certainly produce enough eggs for your family and I'm sure they'll be more than happy free ranging if you can keep predators at bay!