Hi Dragonfly

After my parents separated I did some things that were pretty bad now I look back on them. I can see the reason was because of the separation and my family going in separate directions. A family of 6 living together to 2 of my siblings going on their own, my brother going with my dad, and me going with my mom. We kids slipped through the cracks. I was acting out and looking for attention.
As mentioned, this is a very difficult time for your grandchildren, and it will continue to be for some time. They need some solids in their lives because their home life as they knew it has been shattered. I can tell you're very loving towards them and they're very lucky to have you.
I think it's important they have some discipline in their lives. A huge mistake is to let them get away with things out of feeling bad for them for the situation they did not create (the separation). The therapy I've been in has suggested disciplining kids by taking away a privilege, such as their cell phone or something else if they don't have one, depending on what they did. If it's minor a simple talk when both of you are rational about what happened and emotions don't play into the conversation. Taking a privilege away if it's serious enough. Grounding if it's something more serious. I also think it's important that you and your son agree on how to handle these situations so they have consistency.
I didn't have anyone as a young teen to take me clothes shopping or to get my haircut. I cut my hair on my own (very badly) and wore my step-moms clothes infrequently. Her daughter saw me in them one day and I was scolded to the point that I moved back in with my mom. You and your son need to try to pay attention to your grandchildren's needs. Such things as are they seeing the doctor and dentist. Do they need a haircut or to be taken shopping for clothes and school supplies. Are they being given the chance to spend time with friends.
I know you're an amazing grandmother and the potential is there for you to be your grandchildren's confidant, which they really need. Also consider them having some form of therapy so they can talk out their feeling about the separation and maybe get into groups with other kids experiencing the same things.
Good luck!
Peace