What you have mentioned about your father harassing your wife and your brother's wife is a terrible evil and abhorrent action, especially since your father has reached this age. What you have to do is the following:
Take precautions to prevent this evil, by encouraging your wives to wear covering garments, because many cases of harassment between mahrams occur because of carelessness in uncovering awrahs in front of them. So you may find a woman wearing tight clothes, uncovering her calves and forearms and more than that, on the grounds that she is sitting with her mahrams. But she does not know that the Shaytaan may encourage one to do everything that is haraam, and that a mahram may be tempted by what he sees of the charms of his mahram.
Another part of that is taking precautions to completely avoid being alone with him. So your wife should not stay with your father in a place where they are alone together; rather she should stay with her children or with your brother's wife.
Another part of that is that your wife should object to that and speak harshly to demonstrate her revulsion and anger at your father's behaviour, and not allow him to do evil actions.
Advise your father, even if it is indirectly and without being explicit, if he persists in this behaviour.
If your father continues to do this abhorrent action, then there is no option other than to take your wives out of his house so as to prevent evil and to protect their religious commitment and your father's religious commitment.
You should understand that the fact that he has committed this evil action does not cancel out his right to kind treatment and upholding ties with him. Part of honouring him is to prevent him from doing this evil.
Ask Allah, may He be exalted, a great deal to guide your father and set his affairs straight, and to remove this calamity from you.
And Allah knows best.
Reproduced from Islam QA