In regards to the Mae Ping River Cruise, we just turned up at the wharf, We too, were a party of 4, and they accommodated us on the very next cruise leaving. Our party included 2 seniors, 1 adult and a 6 year old. Each of us thoroughly enjoyed being on the river with its sights, & loved the farm at the refreshment stop. Definitely not to be missed. Good luck. I hope you you enjoy this Thai experience.

I am not the booking agency, just a patron - but in saying that, it is not the high tourist season so you would be REALLY unlucky for them to not have room. Take the trip, it's well worth it.

Tripadvisor passed your question on to me. Not sure I can answer it. Howver, just go there. They were not heavily booked when we did the trip. They also run the tour every hour.