A 2013 vehicle is going to have more safety features than an older truck. As you pointed out in your original post- it has side curtain airbags and all the safety features.
However, you have a 2008 pilot that presumably also has those safety features and the children primarily ride in that vehicle.
Since finances are not going to allow you to continue your lease- are you turning in the van or will you be rolling it into a less expensive lease on a smaller vehicle?
If getting rid of the 2013 entirely, then properly using the children's car seats in the truck will be fine. Many people do it. Just make sure that the forward facing car seat is tethered and both seats are installed properly and the children are seated in them properly. If dd1 is small enough to rear face in your seats, I'd consider turning her rear facing as well, since it is so much safer than forward facing. Having the children restrained properly will make a big difference overall.
If you're changing the van for a smaller car, then I'd use the smaller car for transport if possible. It will have all those safety features, even being smaller. There is a crash test video somewhere showing an old volvo or other large vehicle taking on a small current vehicle, like a fit or something. The smaller vehicle cam away with less intrusion and injury criteria than the big old hunk of metal. Bigger doesn't always mean safer when you're talking 15 years old (with 15 year old technology) versus 2 years old with newer technology.