Is the wife obligated to serve her husband's family if they assist him in his work, and is the husband entitled to divorce her if she refuses to do so?

Your husband does not have the right to force you to serve his family, and you are not obliged to obey him in this matter unless it is a voluntary act of kindness from you. We advise you to discuss this with him gently and clarify that serving his family is not an obligation upon you, and that it is not permissible for him to oppress you by burdening you with what you cannot bear. You can involve some righteous individuals from relatives or others as mediators. If that does not succeed, then appoint an arbiter from his family and an arbiter from your family, as stated in the verse: "And if you fear dissension between the two, send an arbiter from his people and an arbiter from her people. If they both desire reconciliation, Allah will cause reconciliation between them. Indeed, Allah is ever Knowing and Acquainted [with all things]."