is there anyone who can kindly show me when to use the network-clock-participate command?
Is it needed in a router with 2 VWIC BRI (2 ports) connected to the same provider?
If there are slips the best idea is to start doing loopback tests on the links. Make a T1 loopback cable (1-4, 2-5, hairpinned) and see if any of the sides are getting slips.
In your 4 examples, if all 4 BRI ports go to the same clocking domain, they will be equivalent. Many people like to use a preference of 2 in case one goes down as well.
As well network-clock-select, it's needed if you do fax or modem. Otherwise, it's recommended to have but no problems should occur if you don't.