Jayco Swan v Coromal F400 v Others?

Hi. The two brands you mention are No's 1 and 2 in terms of brand sales in the Australian RV market. For that reason I would stick with them. It will depend on what you are towing it with and how extreme you wish to take it. There are also extreme off road versions such as Ultimate, Trakmaster and many others in the upmarket range.
I would also look at the outback version in the first two names. They are not heavy off road units but in the case of Jayco, do have stronger chasis, A frame, wheels, brakes and some fittings. If you drive to the conditions and lower tyre pressures, then they are more than suitable to see and do many varied excursions travelling around Oz.
I would spend a lot of time (In my own purchase I spent 12 months looking at various configurations) looking at what will suit your family and also what you will need to travel comfortably. Things like fridge size, battery power, hot water, gas quantity, and cooking are all important items, especially when travelling with children. Then there is bedding,cupboard space, what extras the kids will need, bikes or a canoe maybe, and where to fit them.
So as you can see, keep doing your research and hopefully it will end up with a unit that the family gets many enjoyable hours of fun and outdoors in. We did in ours so I hope you can too Bob.

I have the outback Swift. A mate has the Eagle.
We both recently went for a two month trip, and except for the young handicapped child travelling with me, all the kids (6 of them) slept in their own tents.
Similar in age to your eldest two.
I found with my 12 year old at least, he thought it better to have his own space.

Have you thought of that option? You, the missus, and bubs in a camper. The older kids in a tent? Could look at smaller campers then.

Funny, we're going through the exact same process at the moment, with the same models of campers. After aa-ing and um-ing about the on-road versions or the "outback" versions, we've decided to go for the off road versions as we expect they would be more durable and would obviously handle unsealed roads/tracks much better.

We have Goldstream Wing 3, which has the same layout as a Jayco Swan. How are you going to sleep your kids? We have 2 and they get one bed end (we got the matress split into 2 so we could tuck them in seperately) and we get the other. If your kids are small enough you could get 3 of them North-South but ours are too big for that. You can use the table as a small sized bed but setting that up each night would get old real quick. You can also get a extra table/bed for the lounge section but same deal, you'd need to set it up each night. Given you want to take it on the beach, I'm not sure a wind-up camper is really suitable. They are almost as heavy as a similar length caravan so heavier than what you might want to be towing on sand. Maybe a soft floor camper-trailer might suit better, more sleeping area and lighter.