I took that early morning bus in Oct 2019. I bought the ticket on the bus from the driver. I was not focused on looking for people with prepaid tickets so perhaps it is possible to get tickets ahead of time. I arrived at the stop in the dark about 15 minutes before departure time and was alarmed to see the crowd of people in line. There was a little cafe behind the stop where I bought a coffee "to go" and a pastry to hold me over in the cool morning temperatures and breeze. I was preparing myself mentally for not getting on due to the crowd but everyone there did get on. The line of people to board the bus falls apart due to the baggage loading process. When the bus pulls up, the driver gets out and opens the covers for baggage on both sides of the bus. Everyone in line, with bags, leaves their spot in line to drop their backpack into the cargo area and then walks back to the new line forming. I unintentionally improved my position by walking to the street side of the bus to put my back pack in where there were no crowds and then re-entered the line/queue. The bus was very comfortable. If you take the bus and want to insure you all get on, I'd suggest you arrive at the bus stop 30 - 60 minutes before it arrives. Bring a coffee/tea and pastry. When the bus arrives and you are at or near the front of the line to the bus door, as soon as it stops, have the 4 strongest members of your group grab all seven backpacks and move about about 10 feet down the side of the bus and stand there waiting for the driver to come out and open the baggage doors. When the doors open, throw in the packs and then come back quickly to join the remaining 3 of your group holding their place in line.
Check Rome2rio.com for bus schedules and other transport options from Muxia. I just looked and the bus is $9 USA and a private taxi is $95 - $120. Travel time is 1 hr 15 min by bus and 1 hr 07 min by taxi. You may be able to purchase tickets on line with rome2rio but I was not successful navigating to the purchase page when I just looked for travel tomorrow. Rome2rio shows the bus carrier website as grupoferrin.com and a phone #: +34 (0) 981 873 643. Use Chrome as your internet browser to get an english translation of the website page.