You may have a grease/oil seal leaking onto the drum causing the wheel to grab... How many miles since they were adjusted?

You Dexter and Alko axles have manual drum brake adjusters. Some trailer axles have automatic adjusters but I have yet to see any. Use a brake adjusting spoon or a screw driver and turn the adjuster, "down and out", (which rotates the side of the adjusted next to the backing plate, opposite side from the tire, upward) until the wheel locks down, back the adjuster off until you can spin the wheel by hand and it will rotate 1 and 1/2 turns, (usually 6-10 clicks). Adjust the front axle then the rear.... Axles must be off the ground to properly adjust the brakes... Road test the trailer before you load up and hit the road, check for any excessive "heat' on any of the wheels. If you've got a wheel "getting hot" back the adjuster of a couple clicks. I can adjust all four of my wheels, by myself in less than 15 minutes and I'm in a wheelchair.... It's SO EASY, a ----man can do it!!