How can one deal with a religious intermediary who causes doubt and division between a married couple, and what is the best course of action regarding the husband's hesitation due to these insinuations?

After the marriage contract is concluded, your sister legally becomes a wife, and no one is permitted to interfere between them except in ways that achieve benefit, and causing corruption is forbidden. As her guardian, you have the right to ask the husband to complete the agreed-upon marriage procedures. If he refuses, you have the right to bring the matter before the court to compel him to complete the marriage or to divorce. The husband is obligated to consummate the marriage with his wife if she requests it and he has no excuse; otherwise, he is given a year's grace period. Try to explain the religious ruling to him with wisdom, but if he insists, then secure your sister's rights.