"My sisters have not been at my house today."
Translation:Mis hermanas no han estado en mi casa hoy.
I believe "... a mi casa ..." should also be acceptable. (I haven't tried it on DL though.)
Estado is from estar (estoy, estamos...) and sido is from ser (soy, somos).. Estar and ser are 2 different verbs with different meanings which translate to 'to be' in english. There is a section in duolingo which explains this called 'to be'.
This is a subject of location. Estar would be used. Ser would be used if it were a subject of condition. Si?