Last year (September) outside of any Covid/lockdown restrictions, My Son and I arranged a birthday party at a pub/club (private room) for the daughter-in-law. 50+ people (approx.) attended. 

We opted to use two portable Sonos Moves (grouped, rather than paired), which were setup on a mobile WiFi router. I used an iPhone as the controller and Airplayed from Amazon Music that I pre-downloaded to the iPhone and it all worked perfectly in our case.

We did not have a single dropout, or problem, during the 6 hours of playback… I did raise up the speakers on a stage and used the available disco lighting for added effect. The lighting really helped with the atmosphere and enjoyment, so I would perhaps try keep that in mind too, particularly for a wedding.

Setting the speakers up and slightly out the way of moving/dancing people helped to ensure a good wireless connection at all times between the speakers and the controlling device. So it can be done but I would certainly suggest setting up and testing the system in advance and think about device placement as you don’t want lots of people getting in the way of any wireless connections. It’s worth seeing how good the WiFi coverage is at the venue, in our case the club WiFi in the region of the stage was poor, hence my reason for using my own mobile WiFi router. 

Anyhow good luck with the Wedding too.

The advice generally given on here to such enquiries is:

DON'T DO IT

Crowds of people can seriously degrade wireless performance. You cannot properly test it.

IMO it is not worth the risk for something this important. 

Thank you both for taking the time to reply. 

It does sound as though its not the best idea, but thought it worth asking nonetheless. 

This is an issue that will/could affect all wirelessly played music at the present state of that tech, not just Sonos.