Hi there,
And welcome Here.
I would just use the AT commands from the nucleo to E5 and same on other end. Don’t over complicate stuff. Make a point to point connection, then send data either both ways or one way at a time.
Full or Half duplex. You have sensors or something on one of the nucleo’s?
If so create a data packet with that info (hex, ASCII)and send it over read and display on the other end.
HTH
GL PJ
wiki has this one;
if you use arduino , look at this thread also;