side mirror folding often gets stuck in semi folded or unfold at all when both mirrors are supposed to work simultaneously?

It sounds like it is binding. Likely from dust and crud in the hinge area on the mirror. What I generally do with them is to use some cleaner to wipe the joint down and then I use a graphite or Teflon based dry lubricant. You just need to be sure to use a plastic safe. If you can't find those you can use silicone spray, but it can attract dust. Then I try to push up on the mirror just a bit, usually you can get it to open a paper-thin area on the outside of the folding hinge. Then spray lube in there. Next push down and spray between the rear of the mirror and the mount. Now fold the mirrors a few times, I try to spray in the hinge area while they move. Work them a bit more and then wipe up any excess lube.