How to use domain name to access my local website?

I have read similar questions, but no answer.

I build a website in a local area network(LAN), it runs perfectly.

Assume that A is server, B and C are hosts which stay in the same network with A. my domain name xyz.com is pointed to A,and works.

I can access website with localhost\xyz.com\IP_A on server A. I can access website with IP_A on host B,C. I can ping xyz.com and it works on host B,C.

but I can't access website by xyz.com on host B,C;and I do not want to edit host file in B,C. My web framework is flask only and without nginx or other web tools. so,what's the problem? I am really confused and waste a lot of time although it's not necessary. Thanks!