You should be able to use the antenna exactly the way you have described by connecting cell1 and aux1 into the RUTX11 accordingly.
Teltonika currently manufactures a couple of devices capable to fully utilize your antenna. These are:
- RUTX12 routers. They have have two modems and four SMA connections, two for each modem.
- RUTX14. These routers have an LTE Cat 12 modem, which is capable of 4x4 MIMO support.