The rule is now that you can transfer out as many times as you want in one use year or, alternatively, you can transfer in as many times as you want, but you cannot both transfer out and in during the same use year. To do it, the transferor has to call MS and give account number to which transfer will be made; best to simply have both members on the call when it is done.
You can transfer only "current" use points, not banked or borrowed; however, recipient can bank the points once they are transfered.