access to win10 laptop from win7 pcs on lan

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A LAN has two win7pro pcs, a new win10Home laptop (replacing an older machine) and other laptops. The two win7pro pcs and the new win10 laptop form a development system for database/app/webapp software, and must be able to create & write files to most any folder on any of the three machines, anytime.

Essentially, we must be able to treat these three machines as if they were just one machine with several drives run by multiple instances of an admin user. That's how we work.

I can hear the corporate intakes of breath. For this request, lose that mindset: we're a family, not a corporation.

When the win10 laptop was configured and introduced to the network a few weeks ago, we managed to persuade it---against its corporate wishes---to allow such access without authentication requests.

Now, the win10 instance has updated itself, and since then, both win7 pcs encounter username & password requests on attempting to access the win10 laptop's drive c:. That stops us cold.

Worse, when the username & password are entered, we meet a further Orwekllian requirement for a password for the drive on win7 machine from which the request was made!

How do we defeat these ludicrous requirements?