Is it wrong to love someone that is family,so confused?

ok im 38 my wife 58 and our her granddaughter 18 the problem is that i think i am in love or lust with her ,she brushes her t,,ts against me rubs up against me all the time shows me her panties when it is imposible for me to look away and walks around half naked in the house making sure i notice ,what do i do?? i have feelings for her and i think she has the same for me ,we do everything together shop cook clothe s omg what do i do ,she talks to my wife about everything and my wifes tell s her all about me personal things ,sometimes i think she is grooming her for us too be together when she is gone,i find myself thinking of her 24/7 while im away ,so confused pleaase help!!!