Probably not the ideal solution, but if you really are playing with your family, and assuming you're all in the same house, you could always play on the same PC instead of using netplay. You'd all want your own USB controllers or something like that, but that would work without any syncing issues.
Other than that, take another look at the netplay setup guide: https://dolphin-emu.org/docs/guides/netplay-guide/
Other than that, take another look at the netplay setup guide: https://dolphin-emu.org/docs/guides/netplay-guide/