The FIRST thing you need to do is settle on a floor plan that works for you. After finding the floor plan you need to actually go and physically see the camper. Then compare that same floor plan (in person) with other manufacturers models.
When you physically go see the various units, your perception changes immediately, if all you've done is look at photos and floor plans on-line. They are always appear bigger in your mind than they actually are. Once inside, they all of a sudden get small. You need to take all 7 of your family members with you when visit the units. You need to actually figure out where each person will sleep by making the beds and then have each one (all laying down), go the bathroom and back. This WILL happen. How awkward is it for each one to get out of bed.
Next, imagine it's raining and you are all inside the camper. How difficult is it to to prepare a meal. Go ahead, have everyone seated at the table, in their bed space, on the couches, you might even take a board game with you and set it on the table for them to mock-up a game. Now? Without the table, how much space do you have prepare meals?
And don't forget about watching a television. When it rains, everyone will want to be able to see the television.
Check out cabinets, storage space, and imagine packing clothes and flood for all 7 people. Where will it all go. If you have to store stuff on the floor or on the beds or couches, it will drive you insane the first time you are caught in the rain.
That's why you REALLY need to go and physically look at each unit and spend time with it, with ALL your family members. Work out the logistics, right there in the show room if you have to. It's time well spent. It drives RV salesmen batty. They want you to settle on anything just so they can make a sale. But, it's YOUR money and YOUR life ... take your time.
If you go through this exercise with every model you've listed above, you'll figure out the "quality" of the RV pretty fast on your own.
The "quality" of any used RV, of any type, is not so important when purchasing used. What is VITAL when buying used, is how well the previous owner maintained it!
Also note, with a motor home of any type, you have to consider not only the RV part of the RV, but you also have to consider the engine, drive train, and chassis, miles on the odometer, absolutely everything, just like purchasing a car or truck.
Another thing, since this IS a motor home, where WILL every one be buckled in at when driving? By physically going and seeing the unit and taking EVERYONE involved with your family with you, THEN you will know for sure if everyone can be buckled in or not.
I'm not saying it's impossible, but you did ask what to do first. This is my list of what you should do "first."
Good luck!