File sharing Between Windows XP and Windows 10

Your subject line says you are using XP and 10, but you filed your question under "Windows 7".  Is there any Windows 7 in the mix at all?

Anyway, I would ask a couple things:

1. Is file sharing and network discovery turned on at both ends?  If unsure, open the "Network" folder (on the left side of file explorer) and it will prompt you if not.
2. Are you able to ping one computer from the other?
3. Are you getting prompted for a password but it doesn't take it?

Your subject line says you are using XP and 10, but you filed your question under "Windows 7".  Is there any Windows 7 in the mix at all?

Anyway, I would ask a couple things:

1. Is file sharing and network discovery turned on at both ends?  If unsure, open the "Network" folder (on the left side of file explorer) and it will prompt you if not.
2. Are you able to ping one computer from the other?
3. Are you getting prompted for a password but it doesn't take it?

1. No Windows 7 involved: I got to that page via a search.

2. File sharing and network discovery are turned on on both Windows 10 machines. All the necessary files (and printer) on the Windows Xp machine are shared.

3. I can ping all computers from each other.

4. When connecting to windows 10 computer a (Toshiba laptop) from Windows Xp via "My Network Places", it requests my Microsoft Account login.  Even when it's visible however, it won't always connect.

5. When connecting to windows 10 computer b (Lenovo laptop), it connects automatically when it's visible but it's sometimes shown as "unknown". If I re-boot the windows 10 machine it will show as available and connects automatically.

6. The windows 10 machines are connected to the network via wi-fi; the windows Xp machine is connected via ethernet cable.

7. When I first set up the network, I could connect from the Xp machine to both 10 machines and vice-versa, but I could only connect from the windows 10 machines in one direction

8. I added the user accounts from windows 10 to my windows xp workgroup. The result of this is that I can communicate both ways for machine a to machine b (but not reliably) but I can't see my workgroup in windows Xp and I can't connect from windows 10 to windows xp.