Folks,
Without getting into the nitty gritty of 'part 4' etc., if there is a one year lease and if the lease itself does not provide for early termination, then the tenant is absolutely entitled to stay put for the year.
It seems to me wholly possible that there is no early termination clause, and that the Landlord simply does not understand that the tenant has an entitlement. This is not to criticise the landlord. Many people do not understand the rights which tenants enjoy under a lease.
The Landlord's son and daughter in law have the trouble and inconvenience of moving to a new home. I don't see that there is any nett gain to humanity by having two families forced into this situation. If I were the tenant, if I were up to date on my rent, and if I were not reliant on the Landlord for anything else, I would certainly stand my ground.