House has issue tenant declined to move out

[Rudy Manna]

I have a house in Washington that has developed a septic issue. Based on the contractor the septic is beyond repair. At this point, we want to move out the tenant and providing generous move out package - one month hotel stay, one month rent back, hold fee for next apartment etc, but the tenant is not -cooperating and also blackmailing us based on situation. They are still living in the house in spite of providing alternative accommodation and potentially further creating mess. They brought in additional people to live in the house who are not on the lease. They are threatening with unreasonable demands such as, give me the money now and I will vacate later else I will cut loose and create havoc.

What are your thoughts? What are the risks?