You can create 3 master pages with different themes and load them dynamically according to your condition on particular page is as below.
Set the master page dynamically on specific page.
protected void Page_PreInit(object sender, EventArgs e)
{
if (your condition)
{
this.MasterPageFile = "MasterPage.master";
}
else{
}
}
For more info :
select master page at run time for a specific page