I am sorry your parents are having such a hard time and I think it's commendable you are there to help them. While I am not a seamstress I can offer you basic sewing advice. There are a couple of problems with the items you are talking about. The pants with the zipper all the way down the side may require a whole new zipper. It could however be a rather simple alteration of opening the leg and laying it flat. Keep the zipper tab up the leg and don’t let it come off the end after you cut off the unwanted leg. Then you would fold up the hem and sewing across the whole bottom of the leg and through the zipper itself. As far as the sleeves go it could be tricky. When you shorten sleeves you must consider how the sleeve tapers. When you cut off a lot you loose the taper and get a much blocker look to the sleeve. Sometimes, depending on the garment, it looks fine that way. If you are particular about these items looking like they did form the store then they probably will need extensive alterations that would require a good tailor.