Being firm but considerate is a good place to start with your boundaries. You could make a compromise for a while, but if your ultimate goal is a date a week, then I suggest you tell them you would be inteding to work towards that because that is where your boundary is. The thing with boundaries is that they are movable, compromise is a sacrifice "for now." At least that is how I look at it.
I would just be my self, ask questions about their life, talk about yours amd check out their body language amd communication style. Its only a second date. I would think there is lots of time to talk about major boundaries and start real negotiation. You barely know him and you don't know her. I would want to know if the dynamic is worth my investing in. If their communication is not like yours or there are other issues that bubble between them, it will come out I would think over some time and a couple to a few meetings. There is no rush.
Take a deep breath and enjoy yourself. She is going to want to know what you will be like as a person outside of boundary negotiation because that is the real you. Maybe third or fourth date along you could get together before and talk boundaries if it looks like he is going to be a keepr for awhile.
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