All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
There is no harm on you –Allah willing –to masturbate with your wife's hand because a husband is entitled to enjoy his wife with any kind of enjoyment with the exception of anal sex or having intercourse with her during menses.
As for using your own hand to help yourself to ejaculate when you have sexual intercourse with your wife, then it is a kind of masturbation.
Allah knows best.