What happens to me if im the co signer on my parents lease for their apartment?

my sister needs a place to stay and they live in a two bedroom with my niece already. the landlords know about my niece and my parents but that is all. They say that if they are caught it will not effect me unless they are taken to court and evicted. I am going to be looking for a new place to live soon and cant afford to have my credit take a hit because they get evicted for moving her in...they have only lived there for 3 months and have 3 months left on lease and they are in good standing with the property management and have always paid rent on time