Powering two 5v 1amp devices from one battery
You can use one battery with one DC-DC converter (e.g. Adafruit Powerboost 1000) to power multiple devices

But the total current drawn must add-up to less than the maximum the DC-DC converter can provide (1000mA or 1A in this case).

I suspect your battery won't last very long. But it depends if the Pi-zero spends much time in some power-saving suspended state.