I have created a wordpress multisite instance and i am able to create new site creating a normal user with subscriber role. I have 3 themes by default in the Appearance > Themes section (i.e. Twenty Fifteen, Twenty Fourteen, Twenty Thirteen). But, i want my site users who create new sites to be able to access only two themes from their site admin panel. Let's say they should get access to Twenty Fifteen and Twenty Thirteen in their site admin panel. Can any one help me into this?
you have to Network Disable the theme.
Disabling a theme in the Network Admin Themes Screen does not prevent that theme being used by a site. It only prevents the theme being listed in the available themes list when selecting a new/different theme.