This can provide equitable solutions for both families. At most the family may have to drop off the children at the neighbors house on a particular day. Work out a schedule which is both easy for your family and your nanny. Assuming this is the avenue you choose and you have found the perfect nanny, never cut the nanny's salary because she is willing to provide service to two families. If anything, increase the base as consideration of her efforts to accommodate both families.
Agencies are often willing to let two families share the expense.
They will however in some cases raise the fee in order to compensate for the loss of a second full time placement fee. Even with this result the fees can be shared equally by two families without the burden falling on one. I would be most happy to assist any one with additional information relating to child care issues. Please feel free to send an email. Think about giving a gift certificate to assist in obtaining a nanny.