Depending upon the size of the house, housing code requirements, etc. the question is whether they are guests or co/ sub-tenants. I would suggest after checking your state's laws, you might tell him to pound sand and to leave your guests alone. By the time he tries to evict you for the extra rent, they will be gone. Then I expect that if you have clear proof of each timely payment of the full (original) rent, the court will acknowledge that he has no case. Then you are ok until the end of the term of the lease.
You need to look at the lease. Usually leases have a clause that says how long you can have people living/staying/visiting in the premises. If the lease does not address it, then I would not worry about it. If the landlord tries to sue you, I think the judge would not look kindly on the landlord given how short a time your family will be staying with you. If I were you I would bring your lease to an attorney that handles landlord tenant issues.
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This posting is not a solicitation, and does not provide legal advice. It is merely the poster's informed opinion. Please visit with an attorney and show her your lease. This posting does not create an attorney client relationship.