Is it considered a sin to expel a husband and prevent him from entering the home, and to repeatedly demand a divorce from him, after the wife discovered his repeated sexual infidelity, and his refusal to divorce, and his threat to revoke the powers of attorney he had given her?

If the husband is in grave danger due to abandoning God's rights, then there is no good for the wife in remaining with him, and she is permitted to seek khul'. The wife does not have the right to prevent the husband from entering his home or expelling him from it if it is his property or he possesses the right of residence. However, if she fears harm to herself, she should leave the house. Unjustified killing is among the gravest of major sins. It is advised to strive diligently to reform the husband and assist him in repenting. If he repents, then live with him in kindness. If he does not repent, then seek separation through divorce or khul'. If he does not agree, then refer the matter to the judiciary.