You should have no problems running two cards from the same manufacturer - I use two different TBS cards (6984 and 6284) which have DVB-S and DVB-T tuners and they work fine under Ubuntu 16.04.
I have tried the official drivers and those from ljalves and for my mixture of cards, the official drivers work better (less continuity errors and noloss of muxes which was a real pain with the open source drivers).
You may need to blacklist the kernel driver (on Debian/Ubuntu this means editing /etc/modprobe.d/blacklist or /etc/modprobe.d/blacklist.conf and adding the correct kernel module to the blacklist) but I would try installing the drivers first and see if the kernel and userland modules get on with each other and if not, blacklist the kernel module so both cards use the userland drivers.
I've written guides dealing with both closed and open source drivers for TBS on my blog - posts below:
"Closed source drivers from
TBS"
"Open source
drivers"