Zigbee and Bluetooth co-existance
You can use 2 radios with a Wilkinson power divider.
You will have to make sure your transmissions don't collide, and the device that is in RX has enough attenuation so its neighbour doesn't cause damage.
Alternately, you can use RF switches and implement separate RX/TX paths.
The downside is that both radios cannot transmit at the same time, but they can receive at the same time, with reduced sensitivity due to the power divider's insertion loss(3db ideal).
The brute force approach is to have 2 antennas, one for each radio. But this will require more space and physical separation of the antennas of at least 1 wavelength.