The answer is generally yes, you can redeem for someone else. The process varies by airline, subject to their security protocols, which are in place to minimize fraud. Please visit the specific airlines website for the rules and regulations applicable.

As to your question regarding selling miles, here on Flyertalk the subject is not actively discussed or condoned. Every program prohibits it.

If you have any further queries on these subject, please send a message to the forum moderators, for assistance.