Seeing Queen Elsa's potential as a force for good, the Friends keyed in to Hans' desire to rule his own kingdom and pointed him towards Arendelle with the goal of usurping and/or killing the Queen. Gaston himself gave him some pointers on how to keep the populace occupied while he did his evil deeds. Hans did so well in winning the kingdom over, that the friends permitted him to save lives rather than let everyone die in the frost, hoping for a kingdom of soldiers rather than nothing but souls. When Hans failed, the Friends promptly abandoned him.
However, the cruel manipulations he pulled on Anna's lovesick heart has not gone unnoticed by the High Council. Because Hans' deceiving appearance and actions before his reveal were similar to that of the other Princes of the past, Zeus has taken an extra close watch on them due to paranoia to make sure that they don't end up revealing themselves to be just like him.