PTP nanoseconds synchronisation between slaves

Question

Given the following IEEE 1588 PTP topology:

• All slaves are identical embedded devices (hardware and software)
• All slaves and the switch has PTP hardware support.
• The GrandMaster does not have any PTP hardware support.

The Grandmaster clock is not connected to any kind of GPS clock, and I don't care how far off it is from the real UTC clock. What is important to me is that the 4 slaves are well synchronized between themselves.

I am looking for a clock synchronisation between slaves in the order of 5 to 20 nanoseconds. The accuracy between the Grandmaster and the slaves does not have to meet this requirement.

Three questions:

1. Does the fact that the Grandmaster does not have any PTP hardware support (like a standard laptop for example) influences the precision I can achieve on the clocks between slaves?
2. Is there an obvious choice for the switch to be configured as Transparent clock or Boundary clock for my requirements?
3. Is this even logical for me to use this not-so-sync-dependent laptop as a Grandmaster? Or should I instead have one of my slaves to become a Grandmaster? The laptop is needed in my system, so I figured it'd be the GM so that all my slaves would be identical entities.