Does leaving the house door open, the presence of one of the sisters to help, and not speaking with the maid except out of necessity, interrupt the unlawful privacy with her?

Entering upon a non-mahram woman when she is alone in a house is considered unlawful seclusion (khalwa muharramah), based on the hadith: "Beware of entering upon women" and "No man should be alone with a woman unless he is her husband or a mahram." As for speaking with her from behind a veil without seeing her, it is permissible if there is no suspicion or softness in speech, based on the verse: "And when you ask them [His wives] for something, ask them from behind a partition. That is purer for your hearts and their hearts." This is also supported by the documented interactions between the sexes during the time of the Messenger and the Companions. It is preferable to advise one's wife or sister to handle such matters.