Unsure where this belongs. Error message on my Mac when parent's PCs sleep.

[Danarchy]

As the subject says, I really don't know where to put this, but since Windows folk are usually more versed in router set ups than Mac users, I thought this would be the place.
Move it if it's not, thank you.

Whenever I go out to my folk's place, they have Windows 7 and a DLink router. While my father was alive, my mother had this same problem. If his machine went to sleep, for her to work on her machine, she'd have to awaken his for her to get on line. And the same for me. I'd have to awaken either of their machines for me to get on line. Now that he's gone, I have his machine off unless I'm updating or using it. So I get this error message when I try to get on line that says something to the effect of, 'IP address xxxxxxxxxx is in use'. So then I get up and go to her room to awaken her machine and I'm back on line. I thought from the beginning that it was a router or ISP issue. They had one ISP that told them that it was because their HP computers had a close 'number' to each other and that was that. She's switched to Charter as her ISP and it still happens. Never heard of two machines from the same maker and near same models corrupting the router. I used to just unplug the router and reboot it and all would be fine, but waking her machine up is easier, though still a hassle.
I suppose the easiest thing to do is get another router to see if that changes.
Any suggestions will surely be appreciated.
Thanks for reading this.

[CimmerianX]

We could start with some information:

Run 'ipconfig /all' from each windows host.
Run ifconfig from the MAC.
From the Win machines, are you using ICS (internet connection sharing)

[Danarchy]

Thanks for the reply CimmerianX.
I know how to run ipconfig/all on the Windows machines, but not ifconfig on my Mac.
And I don't know, yet, if the Windows machines are using ICS. But I know my father had set up his machine to be able to connect my mother's printer and some other things to his. That sounds like it may be the issue.
But, when I get back down there, I'll do the ipconfig on their machines and look up ifconfig for the Mac. I imagine that's a terminal command.

[alexstone]

Try to use ifconfig on the Mac machine

[Danarchy]

Thanks to both repliers. I finally got settled enough to check into this. Still haven't looked up ifconfig to see how to do it. Charter tech told me what I thought it might be and it was. I switched out an old Linksys router for the D-Link router my father had and all is well. For three days now anyway.

Thanks again for the interest and advice.