Thanks all for the guidance. It helped a lot.
Did this today. Didn't use wheelchair for my Mom as we had plenty of time.
Read/understood the info wrong at the beginning. When I got out of the plane from Dublin in T5A, i took the lifts down to - 4 (before going to boarding pass scan for non eu or passport scan for irish in t5a). It took me to walkway but I was walking in opposite direction. When I reached t5b, there was security but didn't let me go as I had boarding pass for Dublin which was in t5a. But nice lady told me to go back and use the relevant lines in t5a and told its just momentary separation.
Only then I realised my error.
From there on, all went well.
Thanks once again.