
I wouldn't really call that socialising. Socialising is going OUT and about, into towns, different places, seeing different things, hearing new noises, smelling new smells -not just living with different people. It's the outdoor experiences of cars, buses, bikes etc etc that makes all the difference -and meeting people then. And a puppy will meet a lot more people going for walks in busy areas than it will being in somebody else's home -and it will feel secure being with someone it trusts during these experiences.
I also can't see several different people training the pup in the exact same way, it can be hard enough to get everyone in the same house to understand the same command and the same routine should be used all the time.