If it were me I would keep the Overlander as it has a nicer interior than the Argosy, and the unpainted aluminum exterior. We started out with a '64 Overlander when our four kids ranged in age from 6-11, but as they moved into their teens we bought a '74 Sovereign
for more room.
To sleep 6 in the Overlander with a double bed we made a platform to make the bed the full width across the aisle and my wife slept there with our 3 youngest. We removed the gaucho from the front and built an L shaped dinette that could be converted into a bed where my oldest slept across the front and I slept along the side. It was crowded, but the kids were small and it worked.
When we got the Sovereign
we gutted it and built a new interior. It's a mid-bath and we put a bunk bed on each side in the back and another set of bunks across the hall from the bathroom. The bunks were just roughed in with 2x4s and plywood for our first trip to see how it would work. In the end we went with a set of bunks on one side and a single bed in the back along with the bunks across from the bathroom to sleep a total of 5. We can always have one of us sleep in the back of truck if we all go camping together, but the older the kids get the less that happens.
Best piece of advice in the thread so far was to do whichever will allow you to spend the most time camping while the kids are around to share the experience. We've camped from PEI to Key West to Alaska and the south-western USA, and never in a trailer that had everything working. It's more important to just go!