“You are in error.” You are mistaken. Lenski asserts that the verb may be taken in a middle sense, “you are deceiving yourselves,” and he may be right.
“because you do not know the Scriptures.” The word “know” is a participle and in this context has a causal sense: “because you do not know” (cp. CEB; HCSB; NAB; NET; NIV; NRSV). To make their argument, the Sadducees were unknowingly misusing Moses’ teaching on what came to be called the “Levirate Law;” that if a man died, his brother would marry the widow and have children by her to preserve the name of the brother (Deut. 25:5-10). There is no reason to assume conditions on earth in the resurrection will be the same as they are in this life. Moses certainly did not teach that they were, so the Sadducees were taking a liberty with the text that had no foundation in truth. Furthermore, the Scriptures clearly teach a resurrection from the dead (Matt. 22:30-32). Even though the Sadducees only take the Torah (Genesis-Deut.) as authoritative, there is certainly an afterlife implied in the Torah. Abraham believed God would raise Isaac from the dead, for example. Moses knew there was a book of life (Exod. 32:32). Furthermore, Job, who lived around the time of Abraham, certainly knew about it (Job 19:25ff). Besides, the Sadducees were in error in rejecting the Word of God spoken through the prophets, saying it was not Scripture.
“nor the power of God.” In denying the resurrection from the dead, the Sadducees denied the power of God. Furthermore, God is not only able to raise dead people to the state they were before, i.e., living, it is in His power to raise them such that they will be different from how they were on earth. On earth, we have a need for children and families, but that may not be the case in the next life. Our fleshly bodies will change. “…the doctrine of the future state was there [in the Scripture], and the Sadducees should have believed it as it was, and not have added the absurd doctrine to it that men must live there as they do here. The way in which the enemies of the truth often attempt to make a doctrine of the Bible ridiculous is by adding to it, and then calling it absurd” (Barnes’ Notes; Matt. 22:29.)