What is the optimal course of action with a husband who accuses his wife of Irja' (postponement of judgment, or believing that faith is merely outward profession without deeds) and excommunicates most people, including her parents, and rejects the principle of "excuse by ignorance," while the wife believes that anyone who displays a ritual of the religion is a Muslim?

The husband's belief that his wife is an unbeliever does not affect the marriage contract unless he pronounces divorce. This is because his suspicion of disbelief is invalid. The jurisprudential rule "Whoever does not declare a disbeliever to be a disbeliever is himself a disbeliever" applies to original disbelievers (such as Jews and Christians) and to those who deny what is necessarily known of the religion after proof has been established. As for controversial issues of disbelief, it is not permissible to declare one who pauses on them to be a disbeliever. Your husband's declaration of you as a disbeliever due to this suspicion is an erroneous extremism. You must be patient with him, advise him, and guide him to scholars.