"Can I travel with my roof vents open during freeway speeds. I'm looking to keep the trailer vented for the dogs during travel.
Family 4 and 2 dogs"

The vent lids are not designed for such use and may be damaged or come off.
I have done this, just barely cracked them open, and cracked the rear window open just a little and it drew dirt in all over the bathroom. I was hoping to prevent the interior from becoming an oven in the summer.

I would be concerned about forgotten something falling and hitting the animal, too.

Anything left in the trailer behind the rear axle will be thrown around. Every vertical movement of the tow vehicle or the trailer causes the back end of the trailer to bounce a lot more than the tower or the front of the trailer. It behaves as a see-saw. I learned to clear the cabinets in the bathroom of all hard stuff. Even some of the clothes on hangers was tossed onto the floor, and we were traveling on good roads.