Welcome to the group.
I hate to be just another nay sayer, but I tend to agree with others here. Not so much about the route (I wouldn't hesitate to go straight over the mountains, through Bend, and out to I-84 at Ontario), but in the capabilities of your tow vehicle.
I had a similar vintage Dodge Grand Caravan. Great vehicle for bebopping around town and carrying stuff, but not so good for towing. Tow capacity is 2000 pounds and it was about all it could do to tow my raft trailer (about 1500 pounds). My guess is that your trailer is a little over 3000 pounds.
Two suggestions:
1 - Fly to Utah. Between the price of fuel and the extra costs you are going to incur to get your vehicles ready for the trip, plus the possible costs due to breakdowns, it would probably be much less expensive.
2 - Leave the trailer and just take the van. Set up a little sleeping area in the van (either on the floor or build a platform to sleep on with gear storage below you), cover the windows with Reflextix insulation at night to keep it a little warmer inside. Shower at truck stops and go out to eat. We did just that many times.
Best wishes and I hope you get to visit your family.
