mothernature, it's no wonder you feel like that - when so many terrible things happening to your family lately.
It sounds like things are going OK though with your SIL's son, though it must have been so scary for you all - the appointment at Pendlebury sounds like a precaution - which is good, it means they are checking him over thoroughly.
There's nothing anyone can say about the death of your nephew's baby that could make it any better. Some things are so sad there is no comfort to be had. If you don't know what to say, perhaps you could just send a card to say you are thinking of them and is there anything you can do? You are not expected to come up with anything that will make it all better - that's impossible, but you can let them know they are in your thoughts.
How are your MIL and FIL now? That was such a shocking thing - the sort of thing that just doesn't happen to people we know.
These things all happening at once, and within your family, are just coincidence - it doesn't mean that more bad things are round the corner though it must be hard not to feel that way. It can feel like everything is crumbling around you but actually it isn't - time keeps passing, you keep going, and life carries on. And that's sometimes the hardest thing of all to come to terms with.
I don't know if any of that waffly stream-of consciousness stuff was of any help. I just wanted to say how sorry I am - thinking of you.