Okay this team needs a lot work I will give suggestions on how to improve each pokemon and if they need replaced. Before I do that I will just say this your team doesn't seem to work together. Volcarona is a sun Abuser and your whole team is just sweepers. From the looks of this you need more help than I alone can give. I suggest subscribing to the pokemon online channel and watching the playlist where Eternal climbs the OU ladder. You will learn so much by watching him. Anyways here is my advice.
Having a deoxys as a supporter is a great idea by USE DEOXYS SPEED it is much better at using entry hazards. Give it Focus sash (so it won't be OHKO'd) and have stealth rocks, spikes, fire punch, and either superpower or magic coat. The hazards are obvious and focus sash gives you time to set up both. Fire ouch is for Forretress (a common lead/counter) and superpower is for Tyranitar (which avoids focus sash with crunch+sandstorm) Magic coat can stop your opponents hazards if Tyranitar is no problem.
Cloyster seems fine (maybe rum hydro pump over razor shell for a mixed set) but you may want to replace it with some sort of defensive pokemon as you have 3 other sweepers.
Gengar is one of my favorites. But he is so weak defensively. However this problem is solved with substitute. It will effectively prevent an attack from doing more than 25% damage but if it does less you keep the substitute for another turn. Now since ghost fighting has perfect coverage the only offensive moves you need are shadow ball and focus blast. For your last move slots have substitute and either pain split or disable. If you pick pain split hold the life orb and that with substitute will make you lose health so you can steal some from opponents with pain split. Disable lets you sub up then if your opponent can break the sub you can disable the move they used to do it (if you run disable you may want to use leftovers instead).
Jirachi seems fine since it is your special wall then maybe replace cloyster with a physical wall like poison heal gliscor. Here's the move set
Gliscor @toxic orb
252 hp 88 spd 164 def (nature sp. atk lowered for def and you may have to adjust the EV's)
Volcarona is better in sun so maybe replace it with a different sweeper like a dragonite or use scizor for revenge killing.
Actually Breloom wrecks my current team. What really destroys me is a set with swords dance, bullet seed (technician and STAB make it nasty), Mach punch and spore. Lose the fighting gem for a life orb and your set
I hope this helps if I forgot anything please leave a comment and if you would like some resources for building future teams ask and ill post the links. Thanks