Not quite, it would be more like stating that your sisters are right now at your place.
"есть" is a form of the "to be"-verb, stating existence. That's how you describe possession in Russian to give new information.
However, есть is dropped when you rather describe properties or quantities (I have a clever sister/I have many sisters). Which makes it a bit different from English "have", which works in both cases,
Yes, sure. This is what makes Russian hard for a beginner who wishes to speak without any trouble whatsoever. There is a limited number of frequent patterns, however.
Here is the whole paradigm, ordered as Nominative, Accusative, Genitive, Prepositional, Dative, Instrumental:
- singular (NAGPDI): сестра́, сестру́, сестры́, сестре́, сестре́, сестро́й
- plural (NAGPDI): сёстры, сестёр, сестёр, сёстрах, сёстрам, сёстрами