If I am sounding frustrated, bear in mind that I have been through a whole lot of investigation to put the computers on static IP addresses and now I am being told not to.
So, I have gone through all the suggestions above and have gone back to automatic IP addresses on all computers and the full range on the home modem. I have checked all the advanced sharing options and all the changes to the Services mentioned. I have restarted the modem and all the computers. The home network now appears to be working.
In order to connect to the internet through the mobile phone hotspot I had to return to the IPv4 settings to again make it get the DNS settings automatically. So I am now apparently back to what the situation was before Microsoft deleted the HomeGroup.
I find it extraordinary that Ms can just delete the Homegroup with no warning and no advice on what effect it will have on home computer networks. This has wasted hours of my time and considerable grey hairs and I am comparatively computer literate. What it has done to those less familiar I hate to think.
No marks Ms.