I have good friends, they are both French living in US (actually the mom has been living in the States for a long time). At home the rule was to speak French but when the kids went to school and start feeling more confortable with English also the parents were drifting slowly towards English. At one point the kids ( 5 and 7 years old) were speaking less and less French so they decide to establish a new rule for the parents and kids: you get points for speaking English, after three points you will have to do an annoying tasks such as tidy the room or clean the shoes. It is working pretty nicely for the parents that will have to do the task anyway and for the kids to feel there is a sense of democracy in the house.
Maybe you could apply to your particular situation.
My friends were french and dutch speaking and each spoke in their own language to their kids until the kids had completely mastered the language. After that things got confusing when they were having family conversations so they changed their system and started doing one week exclusively french, the next week exclusively dutch. When the kids went to school in english they added a third week of exclusively english. This system of course only works when both parents speak all languages relatively fluently.