I was able to get in fort wallace one time without any loopholes or glitches i kinda just walked into the door and it opened and i was able to get loot from the buildings, but then i try with my friend, and i cant get in

You can use a wagon to climb in from the side, it works everytime. Test with your freind

I figured that but then all the wagons were conveniently nowhere to be found the second we looked for one

You may need to invest in a bounty wagon then