For tubes.... two booster balls on two stern eyes with two tubes... Done deal
Two tubes is fun... The riders can 'battle' each other and it's pretty easy to sling one outside while keeping the other inside the wake...
Obviously you have to watch em and don't do any extreme stuff like jumping the wake at high speed because you don't want one tuber landing on top of the other...
The pylon would likely work but as chris said would be a royal PITA in my opinion to have to climb over in the boat.... I wouldn't give up that much deck space in my 30'er much less in a smaller boat BUT it's your call.... Maybe before plopping down the money get some PVC and duct tape and mock it up in your boat just to visualize having 5 people (3 tubers, driver, spotter) cooler, life jackets, tubes, wakeboards, skis, and that pylon in the boat...
Maybe it'll work or maybe you need to lower your expectations for your water sports OR MAYBE you need to be shopping for a bigger I/O boat possibly with a tower.