FixturePropertiesThing.cs

public class MyTest : IClassFixture<MyTest.Fixture>
{
    // Somehow this thing is in scope, as well as the values that come out of it. Also somehow, the generated values gets into the fixture.
    public static readonly IGen<List<Person>> Users = Gen.Type<Person>();

    private readonly Fixture _fixture;

    public MyTest(Fixture fixture)
    {
        _fixture = fixture;
    }

    [Property]
    public void SomethingAboutUsers()
    {
        // Can access _fixture.Users or whatever
    }

    [Property]
    public IGen<Test> SomethingAboutUsers() =>
        from nonExistentUserId in Gen.Guid()
        select Property.ForThese(() =>
        {
            // Can access _fixture.Users or whatever, and they are the same users as the other test (one insert)

            // Can also generate your own stuff local to the test which won't be shared.
        });

    private class Fixture : IAsyncLifetime
    {
        public Task InitializeAsync()
        {
            // Insert all the users
            return Task.CompletedTask;
        }

        public Task DisposeAsync() => Task.CompletedTask;
    }
}