If it were my trailer I would be shopping for new tires. Just sitting without being used is very bad for tires. Look for small cracks in the sidewalls and between the treads. If you see any then get new ones.
There may also be hidden damage inside the tire due to rim rust or other moisture that is inside the tire. Either way, I would shop for new ones and not use those tires.
Also would probably be a good idea to repack the wheel bearings and check/adjust the brakes before you take off.
Barney