I’ve got a gateway deployed in the tower of a local radio amateur without any issues. It is best to make sure the antenna’s not in the same horizontal plane but mounted at different heights.
Yes, you should expect disturbances. But because you are not transmitting all the time on the BOS-frequncy imho this disturbance will not matter to much.
If the disturbance becomes a problem, you can use a gateway in a shielded housing and additional selective filters for the antenna.
Space separations are one of the easiest mentored to use first to try and mitigate interference, vertically, a few meters below or above any other antennas.
If this does not work then you are going to need filters as suggested by @wolfp
It depends on how close you will install your LoRaWAN antenna’s to the TETRA antennas. It is always good to maximize distance. The best position for your 868 MHz antenna is in a staight line above or below the 380 MHz antenna.
Because of the difference in frequency (LoRaWAN is 868 MHz and TETRA in Germany is 380-420 MHz) I do not expect serious influence.