Hrm... I'm definitely watching this case. I think the Snyder family has the right idea- it's not a case of free speech, it's the targetted way they are doing the protests.
Yes, one has the right to say what they want... up to a point. The classic 'fire in a crowded building' case is not protected because of the potential harm it can do. And what they are doing here, by targetting military funerals, is again, potentially causes harm to those in the military, a selective form of discrimination, and, possibly, tryable under hate crimes for a specific group. They're not going to get busted on the free speech issue, that's a bad slope to start. (And thus, why I think the church is going that way.) But, what they can do, is get them for harassment. We have a clear case of slander, with the poem on their website, also. There's plenty of things for the justices to get them on, without making the determination of a free speech restriction.