You could try one big kennel, or a couple of smaller kennels.

But, I would experiment a bit with just the trailer first. Open the top with enclosed sides. Then get the big dog good and tired, and see if they would both stay together in the trailer.

The kids trailers are pretty small. I've built a custom cargo trailer a bit larger which is nice for bigger stuff (and would give more room for dogs, kennels, camping gear, etc.