The rent contract only has two names on it, but I am going to give birth soon, then how much can the landlord increase rent for a newborn baby. And I will need another person to stay for one month to take care of me and the baby after delivery, so how much can the landlord increase rent? The contract only states that additional charge will be applied if a visitor stays for more than a week, but it doesn't state the amount of charge.
Landlord / Tenant Lawyer
There is no "correct" answer to this question.
California only has a requirement of "reasonableness" in this area.
Much depends on the terms of your agreement and apparently the contract is silent on the actual charge. If a rent increase of less than 10% is given the landlord must give you a 30 day written notice or a 60 day written notice for increases of 10% or more.
You may live in a locality with a rent control ordinance and that may control whether any increase in rent is allowed or the amount that can be asked legally.
Consult a landlord/tenant attorney in your area.