This achievement requires a partner to boost for all of the skins. Most of the planes will have the majority of the skins unlock by just completing the campaign. However each one requires victories online with the plane. What you will want to do is set up a private race for the two of you and have one person go through each of his planes to unlock the skins that require a victory online. Most of them you can just go through quickly earn the online skin after a single victory. However, Stallion Turbo, and Spark, require ten victories online with each plane. Also, the plane "Spark" will not even unlock until you play through twenty total races online with any of the other planes.
To set up the match, one of you will will start up a custom match online, and change the settings to 'Survivor Race', 'Strong time pressure', and make a session private. Invite your partner and start boosting. This will take two hours at the most for both players to achieve all online achievements.