In-laws staying in house for 6 months unannounced

[Michelle Tucker]

I would love some advice- I discovered that a tenant in my duplex has had his parents staying in the apartment since August (5 months). The couple had a baby and had the parents there to help out. They will be leaving in January. I was not asked for permission to have them stay and in the lease it clearly states that there should be no additional guests. The water bill has increased dramatically which I have raised to the tenant. I am not sure how to handle this - the tenant moves out at the end of March - Any advice on what I should ask for in terms of additional compensation? I do not want to evict them but I feel that they have taken advantage of this situation.   I also understand that should anything have happened to them- that I would be potentially liable etc. Appreciate any thoughts-