An interesting one.

 

At least 15 large wedding guests pose on staircase to balcony at Holiday Inn for photographs.  I make it a load of perhaps 1500kg+. Staircase collapses.

 

Are Holiday Inn liable?

 

https://www.thesun.co.uk/news/2978934/wedding-guests-rushed-to-hospital-after-10ft-plunge-when-staircase-they-were-standing-on-collapsed-during-celebratory-photoshoot/

 

 

 

Assuming the staircase failed beyound its design parameters, if not them designer / SE / constructor / installer will be liable, and guests were not told  that no more than N people could be on the stairs then Yes because they did not risk assess the possibility of an overload. Even if all 15 of them jumped up together they should not have been there together. It is an example of the Roman legions breaking step when crossing a bridge I guess it's probably not the dead (no pun or insult intended thats just what its called) load that's the problem. All that said it will come down to a bunch of barristers firing expert witnesses at each other.