My young daughter age 7 seen my son 13 masterbate in his room. How do I deal with both of them. This us so awkward. Thanks?

Dont get mad. Be open with both. Suggest that you tell daughter that her brother was "playing with himself and it's something that kids and adults do from time to time" and he should have done it in private. Tell your son that masturbation is normal for everyone, but should be done in private.
Many issues. How old is your daughter? How have you prepared your son for sexual maturity? If your daughter is old enough to begin to know what is going on and is not too young as to be totally naive, then you must sit down and discuss this with her in an appropriate way. You cannot hide nature. You must sit down and talk with your son and let him know the appropriateness of his actions so or the inapprop.