on ninetails, im pretty sure HP dragon provides better coverage and still hits dragons SE though ice hits dragonite better. That power herb would be wasted if you used solar beam in sun though. and politoed is hardly OHKOed by solarbeam off ninetails.
Hmm.... the vena set is hard to say, mix set is OK but i would say as a general rule to have sweepers specialize because mix sweepers are either slow or frail because they need to use a nature that takes away from either speed or a defense stat. HP fire is good for scizor though that lets dragonite wall you cold, having a x4 resist to grass STAB , resisting HP fire and taking nothing from EQ. Completely ignore sleep power, you need coverage, use some strong poison STAB to hit dragons neutrally, keep HP fire since scizor is the most used poke and ferro would cause some troubles.
your volcarana is walled by a rock type, end of story. And from what im told volcarana are bulky. I wouldnt use one though, show me a team without SR and i will show you an idiot.
dragonite needs roost, maybe ditch DD if you dont want to get walled, but get roost on there, abuse that bulk, especially with multiscale. but if you choose to ignore roost you need leftovers, i wouldnt ignore roost though, most people dont. I mean at +2 dragon claw is effectively neutral on anything.
i would psyshock on espeon since only dragonite could touch blissey, use morning sun for recover since it heals 2/3 in sun.
scarftran isnt the best revenge killer in the world, maybe put extreme sped on dragonite for that purpose. Heatran could probably do better with SR(you will need this)/lava plume(burn chance)/earth power(counter oposing heatran)/roar or toxic. i disagree with the earlier suggestion of dragon pulse as dragon pulse is weak and next to useless without STAB.
terakion trashes your team too. Stone edge hits half your team super effectively while hitting the rest neutrally, espeons low defense wont stand against a neutral attack(plus the thing carries x scizor) and heatran is KOed by close combat. The only thing hit neutrally here is venasaur, i dont know what other move terrakion carries but there are 5 more teammates to kill venasaur. fix the rock weakness should be first priority, get rid of one of the three ones weak to it and add a resist, nothing on your team resists it.
this may seem a dumb suggestion given this poke is LU but try scarf typhlosion over heatran, it can easily revenge kill with 150 BP STAB eruption, which is 300 BP in sun with STAB factored in, complete coverage of weaknesses in solar beam and focus blast to kill things like heatran and that rock weakness i told you about, then you have one slot left over for more coverage. HP dragon perhaps? or maybe flame thrower for when typhlosion is lower on HP.