According to this link the nominal output power of the speaker is 80 watts, if that’s what you require:
https://www.cnet.com/products/sonos-play-5-speaker-wireless-play5us1blk/
More importantly, use of wireless speakers isn't recommended for events like weddings because of the chance of music play stopping when you most need it.
Power varies so much depending on the music being played and the volume I’d hate to guess.
Buy a Kill-A-Watt meter for $30 and hook them up to it. Give then a test run doing exactly what you plan to do for the event and the Kill-A-Watt will give you the needed power.
I’d be wary of wireless too, bodies absorb WiFi and what worked across an empty yard can fail with it full of people. Same for an inside room too and testing is hard.
Long Ethernet cables and AC extension cords are cheap compared to a battery/inverter setup and might be more practical.
http://www.p3international.com/products/kaw-chart2.pdf