How to expand an Arduino when using a TFT display shield?
As I can read your link, the shield is using D2-D8 and A0-A3, leaving some pins unused. So some Arduino pins are still free to use, just the shield is in the way to get connected there.

So there are some possible ways:


brutally solder some wires to the shield unused pins from front side and use that wires to connect where you want (sensors, breadboard, universal PCB, ...)
brutally solder some wires to arduino bottom on unused pins, then continue as mentioned
create intermediate shield (there are many, which allow you connect to arduinou on bottom and stack antother shield on top, draw your wires from there (and maybe even put some circuities on the middle shield, if you want 
(something like this https://www.aliexpress.com/item/UNO-Prototype-DIY-shield-kit-for-Arduino-UNO-Universal-Extend-Board-UM-UNO/32555004112.html or any "arduino universal shield" 


https://www.indiegogo.com/projects/ardushield-most-universal-shield-for-arduino-ever#/ works excelently across arduinos and other shields/breadboards ...

or anything along this lines ... http://shieldlist.org/sunhayato/universal


use pins D10-D13 as they are connected also to ISP header https://www.arduino.cc/en/Tutorial/ArduinoISP and could be connected from there. As they are part of SPI interface 
https://www.arduino.cc/en/Reference/SPI that could be good coise too (if you manage ChipSelect somehow.




As for other part of question - 
It is possible to connect more arduinos, there are so much different ways, that it is hard to write here all - choose one, that would suit you best. (anyway you would need some access to some pins anyway )