I think the US, and it's allies must do whatever is necessary to form a coalition whose primary goal is to destroy ISIS. If that means some degree of accommodation so be it. The goals of various nations vary widely, for example:
The Saudis refuse to engage ISIS until, the other powers agree to remove Assad. Israel refuses to enter the fight until the US does something about their enemy Iran who is engaged in the fight against ISIS now. Although Iran is fighting ISIS, it is also a strong supporter of Assad who Turkey wants ousted because Syria Kurdish forces threaten their boarders. Now the Kurds want only to stop ISIS with little interest in what happens to Assad. Iraqi's main purpose is to link Iraqi Sunnis to ISIS by only using using Shiite fighters against ISIS. Their opposition to Assad goes only as far as required to placate the US. Syrian forces are deeply divided over their support for Assad. Those forces that support Assad are fighting ISIS but so are some of the forces that oppose Assad, who are being attacked by the Russians who support Assad but now are attacking ISIS.
To make this tangled mess into a coalition that's working together to destroy ISIS is going to take some real statesmanship and compromises.
It's not all that complicated really; just break up and/or weaken the Iranian allied coalition and things quieten down significantly. The rest fall into some sort of order after that is achieved, as they are little more than tribal and clan politics jockeying to be in favor with who-ever is winning at the moment. They can't really be considered to be as important as busting up Iran's meddling and destabilization strategy.
Putin's interests are his little naval base and destabilizing and baiting Turkey; whatever one feels towards Turkey there is no gain in allowing Putin any excuse to start bullying Turkey. Whatever issues the EU or the U.S. has with Turkey can be dealt with after the important problems are fairly well settled.