Dave Plowman wrote:

Win 10, it can see and share with the laptops, but not the other way round.
And since I've got 4 computers I've recently updated to Win10, they're all
set up in the same way.

Were they wipe and install, or upgrade, if the latter then differences
will have been carried forward.

under control panel/network & sharing centre/change advanced sharing options

have you got network discovery and file/printer sharing both turned on
for the "private" profile (assuming your PC does think it's on the
private profile, which it ought to)