Replacing tenants on lease- room mate drama

[Jessica Gilbert]

(Texas) I rented a 3/2 to two sisters and a couple who looked just fine on paper.  Everything was quiet for three months until the couple started blowing up my phone wanting off the lease. After speaking with the sisters, I decided my best course of action would be to screen two other women who the sisters said would like to replace the couple on the lease. They have passed screening, but the couple got angry and left before I could get them screened and now are ignoring me. They told me they are just breaking the lease. I guess since they said they are breaking the lease, they think they don't have to do anything else. I only need them to sign the paperwork removing them from the lease so I can add their replacements. If they refuse to sign anything, what the heck do I do? I can't just add people to the lease without their permission if they are still on the lease. I don't know if I can just end the lease and start a new one with the new tenants... I keep reading and can not figure out a clear solution that keeps me covered legally. I have been assured that the next month's rent will be paid by the sisters. I thought I had most scenarios planned for, but this one is throwing me. Any help? Thanks so much!!!