Should I get a different camper

Look at it this way, the cost of a new camper is going to be $3000 more because of the choice you made initially, which was the best choice you could make at that time. Is it possible that you could use a tent for the daytime for the pack and play? Also unless you have air or are using heat ANY camper will still have that "damp feeling". When growing up (centuries ago) I knew of families of 6-8 who lived in homes with less than 600 sq ft.

You also don't say what size pickup you have now. That will determine the size of 5th wheel you will be able to get. Also as those kids get bigger consider if you want bunkhouse, or are willing to convert the table and sofa to beds.