I am just confused why it is called Co Star. Do you get faster through the Coop mode? Had it rather divided as in Smg2 in 1P/2P

co-star mode (what in the community is often referred to as 2p or 2-player) is when you have a second wiimote usually attached to the first one that allows new movement options including being able to get extra height whilst in midair (midair 2p jump), as well as extra height from a grounded position (grounded 2p jump) as well as making star bit collection easier and a few other features which do make running 2 player faster, until a few days ago on the leaderboard it was labelled "players" and then with the options "1p" and "2p", this was changed as some questions were brought up regarding having multiple players perform the same speedrun and so the names were changed to "co-star" with the options "yes" and "no" to be more clear

How do you stock the right joy cons together before any co star runs

If I'm understanding your question correctly, people tend to have velcro dots/squares stuck together acting as separators. Here's what my and most people's setups look like. The red joycon is the Co-star joycon.