Can all RX and TX chips be made compatible with each other?
"Q.1) Is it possible to use RX / TX chips from two different toys together?"

Maybe, if the two chips use the same protocol and frequency. In the old days, with 27 MHz radio controlled model planes and such, there was one dominant protocol and the only variation was the 27 MHz sub-band that was used, so exchaning a crystal ws often sufficient. But those days are long gone, and there are lots of cheap chips that implement different protocols.

"Q.2) If possible how can I do so?"

Most probably we couldn't, so you definitely can't.