Parents: help me parenting while separated (2)

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Today is Thursday so I have to kids with me.
As usual, I went to STBXW's place to pick them up. On the phone I immediately sensed something was not right.
S9 came downstairs first. He was angry and had been crying. He didn't want to tell what had happened and told me to ask mom.
She came moments later. She was bitter. She said that lately S9's behaviour has been unacceptable. Today he had asked for her computer and after a refusal had said some nasty words and thrown the door. STBXW also said she was very tired. S9 would not ask for things in a polite way but instead would demand them from her.
I called S9 to my side. I put my arm around him and told him to listen to his mother.
When we left to my place S9 said he didn't want to ever go back to his mother's house. He asked me if I had some knives at home so that he could kill himself and end his mother shouting. He complained that STBXW is always shouting at him.
After dinner I had a short talk with him. I asked him if he was still angry at his mother because of the separation. He said yes. I replied that it was good for him to acknowledge that anger and express the feeling, but that we needed to find what to do with it.
Because it was bed time I said we would speak better tomorrow, since I will be having them for the weekend.
Any advice on how S9 should deal with this, parents?
(I don't consider worrying S9 talk about killing himself. He said that without fully understanding what is suicide and only as a way to express his anger.)

On a brighter tone, the three of us started practising yoga we with a nice lady we found on internet (just google Cosmic Kids Yoga).
And right before going to bed we watched a National Geographic program about airplane accidents. This program had a notorious impact on them.
It was an interesting moment. After the aircraft had safely landed I introduced the theme of life value.
I told them we should always appreciate life and what it had to offer. I said we should be grateful for our relatives, friends and what we have.
The kids fully understood my message.
With them tucked in bed, I asked S7 and S9: "What are you grateful for today?"
S7 said "My friends" and S9 "Life".