Playing Nice?

I wonder if anyone out there has constructive advice on sibling play.  The kids are just getting to an age where they are interested in some of the same things and can play together.  What I don't have a good sense for, is when I as a parent should jump in and mediate screaming, screechy disputes and when I should just back off and let them figure it out or take the fight to its epic meltdown conclusion. 

A few nights ago, the kids were playing and after a few minutes of screeching, J. checked in on them and Max had his feet locked around Ginger's neck.  Other times I feel like Ginger screeches just because she knows it will get someone to run into the room and she likes the attention.  Neither scenario is ideal.  How do you navigate sibling mediation?

We have now reached that pre-halloween time when the kids wants to
wear their costumes every day.  Here they are playing in the
garden and picking tomatoes for dinner.