If a female 10-12 was asked to take off her clothes while 18 year old brother watched is that considered rape or molestation?

Boundary problem: What you describe would not meet the legal definition for "rape, " but is edging towards molestation. Those criteria usually involve unwanted touching also. Asking a younger sister to undress while the brother watches is definitely an invasion of the sister's privacy, and can cause her deep distress. Younger sisters often want to please older brothers, and may submit to exploitation to do so.

Inappropriate, not rape: As i see it, if nothing else happened, 18 yo asking 10-12 yo to take off her clothes was not rape, per se; and it was definitely very inappropriate behavior. For starters, recommend keeping them from being alone together as well as individual and family therapy for all involved as a next step in sorting out exactly what happened and what further interventions are indicated. Ask police to investigate if 18-year-old is not in family.

Insufficient evidenc: Also insufficent letters. The issue is serious and important, but way more needs to be known before a charge of rape or even child sex abuse is clear. But a non-inflammatory report to child protective services is okay to make on suspicion or concern alone. Was the girl upset? Although even that may not matter. The social workers can advise you. Call your local agency or 1-800-4-a-child for advise.

Not Good: This is inappropriate and could be exploitive. Female should prob get counseling to determine if something more has happened, and for prevention, assertiveness training, education, etc. Brother certainly needs counseling/assessment, as well. Family counseling advised, possible reporting of child abuse