Make the sentences passive.
1. We usually seek legal advice when we sell or buy a house, draft a contract, set up a business etc.
2. Governments make laws and enforce them against citizens within their power.
3. Public laws ensure the authority of the government itself and civil laws provide framework for interaction among people.
4. After the accident someone called the police and they arrested the drunken driver.
5. The police will arrest violent demonstrators. So, if you are violent, they will arrest you. They can keep you in custody for 24 hours and may question you about your activities.

1. Legal advice is usually sought when buying a house, drafting a contract, setting up business etc.
2. Laws are made by government and enforced against citizens within their power.
3. Authority of the government is ensured by public laws and framework for interactions among people provided by civil laws.
4. The police had arrested the drunken driver after they were called by someone after the accident. (Здесь я не уверена)
5.Violent demonstrators will be arrested by the police. You will be arrested, if violent. You can be kept in custody for 24 hours and asked questions about your activities.