My son & his wife are separated

Bear with me for posting here. My son and his wife have just split up. They have 2 little boys -- 4 and 1 and they all live about 4 hours from me.

There is so much, suddenly, to navigate, like, who do I contact now, about seeing the grandkids? They are with their mom. My son is being very uncommunicative about this, which is his right as an adult, but it doesn't help me know how to figure out how to best handle seeing his kids.

Thankfully, I'm in contact with the other grandmother, who is being super supportive of me seeing the kids. She has even offered to drive them 4 hours so I can be with them, and we can take them to the zoo or somewhere near my house. She doesn't want to step on my son's toes, but I am feeling like nothing is going to stop me from seeing them, or from forming a good relationship with their other grandmother, who lives very near them and sees them a lot.

Do any of you have any thoughts from the perspective of a divorced parent, or even a child of divorced parents?

Thank you all for understanding.