You'll have enough power, so that's not an issue. The issue is a family of 4 towing a trailer that's already going to be maxing the capacities of the van. Keeping in mind that the kids are growing and so will their need for more toys.
We towed a similar trailer with a mini-van for a family of 3, and our daughter was in her teens at the time. Not too bad really but you have to watch what you pack. But when we got a bigger tow vehicle it was a night and day difference. The ability to take more things with us and not be limited on things we could buy on a trip was well worth it.