Brian;
First, the trailer was manufactured by Hunter but when the 260 came out, they contracted the building of the trailer to Magic Tilt. As for parts, hopefully I have the right names for parts.
The wheel is mounted to a wheel rim which is mounted to the wheel hub via lug nuts onto studs that are permanently mounted into the hub. The brake drum plate or plate drum is mounted over the axle spindle via racers/bearings. The hub is mounted onto the spindle with another set of racers/bearings which is then held in place by an axle nut.
When replacing the entire assembly, you have to state if it is right or left hand axle assembly.
In your case, a little rust will not hurt but what has happened, the lug nuts are either tightened to tight and/or rusted for better lack of terms onto the stud. Sometimes when taking off the lug nuts, the threaded portion of the end of the studs have been damaged. Either way, I use to put on WD40 or PB Blaster lubricant to loosen up the threads which needed to be soaked by simply multiple applications over a period of time. I use to try then to break it loose by use of a lug wrench going backwards and then forward but forward only a little. Sometimes I had to heat up the studs/lug nuts but be careful if doing that.
You now have a couple of broke studs. I would then take the other lug nuts off and remove the wheel rim. Again, I would lubricate and heat and then try to remove grabbing what was left of the stud and again back and forth. If broken off to the rim, I would have used an easy out and if that failed, I would replace the drum which is costly.
To identify, bearings were generally 1.98 inches or most of the time referred to as two inch. Also, the size of wheel for example an R15240 which means the rim size and the 240 for lack of terms the size tire. Usually somewhere the axle is stamped with the mfg. and model of axle but that may be corroded to the point that you will not find it. Also mention the number of lugs too.
The forward axle had brakes only but inspection if never done of the bearings and racers if you do not know the history need to be checked and if you do not know how to do that, get someone who knows. If bearings are bad, automatically replace the racers/metal pieces that the bearings go round and round on as well as the bearings usually sold separate or together. If ever submersing into salt water, always rinse off trailer, wheels and axles.
If brakes, have them checked along with the fluids activating the brakes. If worn down, replace and have the hub checked to see if the inside surface is rough and if so, have them what we call "turned" to be smoother out.
There is a lot more but if ever putting back on the wheel rims, apply the nuts by hand if you do not know how to torque them on correctly. I hope this helps you sir.
crazy dave condon