A husband smokes indoors even though his wife is pregnant and there are young children. What rights does she have?

She is entitled to ask him not to smoke inside the house or near the family, because cigarette smoke harms others and Islam forbids harming others.
The Prophet ﷺ ruled that there is to be no harming of oneself or of others (Sunan Ibn Majah 2340), and the National Fatwa Committee Muzakarah has ruled smoking forbidden because of its harm. Second-hand smoke is dangerous to an unborn baby, infants and children. Practical steps: agree on a smoke-free home and car; encourage him to use the quit-smoking service at a health clinic; and praise every effort. Avoid constant nagging, but do not compromise on the children's safety. The husband should also recognise that protecting his family from harm is his trust (at-Tahrim 66:6). See the question on smoking and vaping.