Must be difficult, knowing that your 14 year old sibling is being subjected to men in your moms home that are closer to 14 than I'd presume someone in their 40's? (based on you being 24). [add: especially with alcohol involved]
I can see the concern. At the same time, what can your dad do, to ensure the safety of his youngest child, emotionally at the least? Isn't this a conversation he should be having with your mom?
Hoping the best for your family