Nanny / Au Pair Job: Family Profile

We've lived in Central London for 4 years, due to my husband job. We'd like to preserve our children' English knowledge, otherwise they are going to forget what they have amazingly acquired in England. Our idea is to have a native English speaker for few years, so we expect to change au pair every 6/8 months or better, one year, or more.

We are going to come to London to meet and interview our future au pair/tutor.
We’d like to host someone with an exceptional written and spoken English, and possibly some knowledge of another language or a musical instruments (piano/guitar).
We have been living our second au pair experience since last August. Our au pairs have been wonderful, enriching our daily life, as part of our family.
They have done an excellent tutoring activity with our children. They also have a TEFL Cambridge qualification that has given the opportunity of earning some extra money.
We prefer to have a person who loves countryside and first of all, enjoys spending time with children. Our guest is going to have her/his own bedroom and bathroom, wireless connection.
We offer a weekly pocket money, lodging and boarding.
We prefer someone with a British accent, able to to support our children in the KS1-KS2 English Primary School Curriculum, we are going to provide teaching material.
Italian language courses available in the area. We request 28/30 hours a week, recent and enhanced CRB, references.