My wife talks to our daughter and grandweans on Skype every other day. Occasionally ,I want to join in using another computer on the same router. I cannot find a way to do this. Are there any experts who can advise me. Words of of one syllable please.

Not words of one syllable , but Skype tells you how to do it here:

https://support.skype.com/en/faq/FA2831/how-do-i-make-a-group-call-in-skype-for-windows-desktop?q=Using+skype+phone+and+computer+at+the+same+time

Not words of one syllable , but Skype tells you how to do it here:

https://support.skype.com/en/faq/FA2831/how-do-i-make-a-group-call-in-skype-for-windows-desktop?q=Using+skype+phone+and+computer+at+the+same+time

This refers to sharing from another location, I am trying to join in from another room in the same house using the same router

If you are logged in as a different user, no problem just join the conversation.

Not words of one syllable , but Skype tells you how to do it here:

https://support.skype.com/en/faq/FA2831/how-do-i-make-a-group-call-in-skype-for-windows-desktop?q=Using+skype+phone+and+computer+at+the+same+time

This refers to sharing from another location, I am trying to join in from another room in the same house using the same router

It has nothing to do with the 'router' or what network you are on. Each Skype session will have its own connection. Just follow the instructions in the link given