Hey Izz,
I remember from your brother and SIL's email that they sound like kind, decent adults now.
Whoever they were back at that time, they're probably very sorry about. Good for you for gently giving them the chance to tell you...they were ignorant and afraid, probably.
It may bring you closer if you tell them you need to revisit that time briefly...and see if they can "meet you there." I think maybe the most important thing is to keep it simple:
I was so alone, and afraid.
I couldln't understand why you didn't come to visit me.
Can you explain what you were thinking then?
Maybe something like that.
And then get into the present with them, Izzy hon. Please don't forget to be in the present. Hopefully y'all will drink some good wine, play some good games, and be together in the present, too.
hugs
Hops