Tenant won't leave after a fire and utilities turned off

[Rawn Wilson]

I am renting a house that has a detached efficiency apartment in the back.  At first, the tenants in the house were using the apartment for their daughter.  She moved out, and they sublet it to someone else.  I did authorize a sublease in the main lease, but only with my written consent.  I never gave written consent, and no formal sublease was ever established.  

Now, the main house caught fire and fire department removed the main electrical meter until house is repaired and inspected.  The cause was an accidental electrical fire.  The electric supplies the house and apartment.  The main tenants are moving out, but the people in the back apartment refuse to leave.  I will be cutting off all services to the property to make repairs that will take atleast 6 months.  I understand the normal eviction process, but what other means do I have to get the squatters out?  I have researched a sample "Notice to vacate due to non livable conditions", but have not found anything.  Any help would be appreciated.  Property is located in Pearland, TX.