As far as garuda is concerned. Never take both sup and spiny. That fight is all about managing your hate level. Spiny will always target whoever is second in hate which should be you if you're off tanking(sword oath and no defiance may put you under a healer or dps so watch your hate and manage it carefully).

If you do that properly you'll always have the spiny first and both tanks can provoke off each other at the same time. If all you do is shield lob the spiny it will not come to you because whoever it's on has a huge hate lead from the start. If it's on a healer just leave it there so main tank can grab it when it's time. If main tank somehow gets stuck with it, which does happen, just voke the spiny. Once chirada is down there's no more double ww so you don't really need to take sup. Spiny Will cause a wipe so it's the number one priority. Just make sure to communicate so everyone is on the same page.