My ex's girlfriend has just kicked off with my mate, should I get involved?

My mate was out and being civil with my ex then his girlfriend started kicking of shouting all he wants is to see his kids. I talk to my mate about everything and she knows how much effort he puts in to see his kids, so she said to my ex come on now you know you haven't done enough for your kids, to which he didn't answer her and his girlfriend was still shouting at my friend.
The girlfriend had walked off and my ex had spoke to my mate he knows he hasn't done enough and will do the mediation now (iv been asking for 2 months now). Anyway his girlfriend came back kicking off again shouting at my mate even though she had asked her not to shout at her.
My ex takes drugs (coke) and is normally a mess but my mate said his girlfriend was in a real bad way on drugs and drink. she looked a mess she said.

So by getting involved i mean bring this up at mediation?
I have been told that they are messy most weekends and to me they can do as they please my only concern would be that they do it when he eventually has access to the children.
All the children have only met the girlfriend once and they are planning on getting a house together.

She has no responsibilities so i know this can go one of many ways. He hated me going out and him having the kids so maybe she won't want to stay in if he has the kids, which will course arguments

Or they stay in and drink which then comes the drugs

I know i have to give them the benefit of the doubt but they are my children and i really wouldn't want harm coming to them.
He hasn't really seen his kids since getting with this girl would say he's having them and not turn up and we are not allowed contact changed his number and everything
So thats thats why i chosen mediation. Im just worried about this situation now
My ex's girlfriend has just kicked off with my mate, should I get involved?
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