1- No they cannot. They must do them themselves.
2- For the deceased, you can find people to do them overseas in Iran or Iraq. If it’s not too many years, I can help in arranging it in Iran. You may also contact the office of your Marja’ and arrange it with them.
Usually the deceased writes in his will how many days he missed. If he didn’t, then go with the lowest estimate. Let’s say you don’t know whether the deceased missed 5 or 10 years of prayer/fasting. You are sure of the 5 but you don’t know if it’s 10. Just go by the 5 and have it made up for the deceased.