Router- https://mikrotik.com/product/chateau_5g#fndtn-specifications
So one question about this router, is the both external antennas that ar included in the box are for connecting to ISP server/tower?
The antenna’s are used for both 5Ghz and LTE frequencies.
Not the answer that im looking for 
Short Answer: Yes
so in that case i can use both of my directional outdoor antennas that i have and connect them both to this router and i will have better receiving signal strength?
correct me if i’m wrong!
this and first question popped in my head only because the ISP tehnical guy that give me this router said that one of the antennas are for connecting to the tower and second antennas useage for to give better wifi coverage!
I don’t have the Electronics knowledge to answer this question…
I don’t know if you need to change something before connectiong the LTE-Antenna
I just know one of my German supplier wrote under the Chateau
“Sie können 2 externe LTE-Antennen” translated-> You can connect 2 LTE-Antenna
(https://www.mikrotik-store.eu/de/mikrotik-chateau-lte12)
If you don’t get an answer via the Forum in the next couple of days.
Ask your distributer or Mikrotik Support directly