Sorry to contradict the above comment, but I have some experience with this as well. This is more common than most people know.
I'm due may 25th, and on my last ultrasound, the Dr. also found a cyst on my son's brain. It's estimated to be found in 5-10% of babies and we were assured by our Dr. saying that they mostly resolve by themselves before birth, but that even if they don't resolve by birth, they don't seem to affect development.
Our Dr.'s son even had one and he's now a healthy, normal 14 year old.
There is some evidence that suggests that the development of cysts may be normal part of brain's development that may go undetected. So, all of that is positive news!
There is some potentially negative news, however. The reason why Dr's even mention the cysts (which are considered benign in themselves) is because there is a potential correlation why Downs and Trisinomy 18.
My previous tests had shown such a low risk for either of these conditions that we were once again assured it wasn't something to be super worried about. It is important for me to say though, in the ultrasound they looked at the rest of the baby's organs, hands, nuchal folds, etc, to make sure that there weren't any other possible markers for genetic disorders (fortunately, in our case there weren't)
It seems like, for your grandchild, there isn't sufficient evidence to be overly concerned, but to be watchful. In the next ultrasound, they'll look for all of these markers again, I'm guessing, and that new information will help. If it looks continuosly worrisome, it makes sense the parents to speak with a genetic counselor who can help to alleviate their fears or give them information to help as they prepare for their baby, or even help them consider a amnio for further testing.
I know it can be hard to wait for additional info, but that's really all that can be done at this point.
I'll keep my fingers crossed for a healthy grandbaby for you!
I'm currently expecting our 3rd child and our familys are overrun with kids and I've never heard of those things happening or being normal, the kidney doesn't sound too bad but if the cyst is still growing(or even if it's still there) I would get a second opinion to make sure. I hope your grandbaby turns out perfectly fine.
We do not have the same concerns so I can't speak to the exact conditions you mentioned but we are currently monitoring a few issues of concern with our little one. They involve growth, which is best monitored via ultrasound, so I would suspect for the issues you shared, that their medical advice is sound.
As for what you can do, unless your son and daughter in law have asked for your input/advice on how to proceed (e.g., they doubt their medical provider's care and/or have invited you into the decision-making), I would suggest trying to be supportive, be a good listener, and do not question their decisions. If they are anything like my husband and I, the last thing they need to hear right now is that someone doubts the medical advice they are following! If they receive results that they share with you, thank them for sharing and ask if there is something you can do to help. If you have the resources, maybe send them flowers, buy them a giftcard for a restaurant they may not pay to take themselves to, etc to give them a surprise some day. It doesn't have to be monetary - one of the nicest things a friend did for us when we had a period of high stress was to take our dog for a long walk and drop off some extra food she had made for dinner.