
Shocking!! And I've been in on C.Sections - right there. Never have I seen anything like the clamp you describe and in my untrained view, of course this could have cause hernia. Each of my puppies had the cord cut, not left long.
If there has truly never been this kind of hernia in previous generations .... YES, take them to Court. Or at least report what happened to the Veterinary Regulatory bodies. I would caution re cost of suing. You may be better to cut your losses, and walk from that Practice, with your feet? IF you get a good outcome it might help re the owners of the puppies - are you going to have to pay for the hernia repairs which are usually done at the time of neutering, if that's done? That might influence whether or not I took this further, legally.
As I see it, you are most concerned about the reputation of your (and others behind your line) bloodline re hernias, understandably. You won't do that even if a case went your way, with compensation (money). So I'd be reporting this Practice/vets to their regulatory body if they are likely to use these clamps again, although you'll most probably be told this is standard practice. Seems to me it had more to do with the cords being left too long so the puppies scrabbling around, dragged on them, which could quite likely have involved tugging at the umbilical cords, causing the potential for a hernia.
At the end of the day, it depends on who pays for correcting these hernias - and, if you, that might be worth going after your vets for (compensation).
Talking to Trevor Cooper may help.
Good luck - it's traumatic enough to have a bitch need a 'Section AND be spayed at the time because of the rupture, without now being accused of having a line prone to umbilical hernias?