I went through this headache recently myself and discovered that followers can not use higher level spells until they gain the appropriate skill level. Once they level up some, if you check the PC mult box to enable auto leveling on the stats tab, they should be capable of using the new spells. Also a lot of perks do not actually work for followers. For example a follower will benefit from the first rank of magic resistance in the alteration tree, but will not benefit from rank 2 or 3. Lookup dragon priests in the creation kit to see all the useful mage related perks a follower can actually use. Also be careful when assigning left or right hand versions of the spells, it can make them bug out in combat if you choose poorly. Also from my understanding npcs can not use any spells that require both hands to cast like master level spells. Hope this helps.