Like that: Ola Kowalska -she Piotr Kowalski -he Rodzina Kowalskich -Kowalscy family Państwo Kowalscy -Mrs Kowalscy dom państwa Kowalskich - Mrs Kowalscy's home :-)
is hasn't always been the case. there are families that still keep the masculin form of the last name for all members. it's the evolution of the language that has instroduced this differentiation between men and women in a family.
when you marry you can actually choose the form of your 'future' last name.