Books written in a letter or diary format with multiple POVs or at least character perspectives

[Emily]

You probably already know about The Guernsey Literary and Potato Peel Pie Society
Here's a thread you might find useful
Epistolary novels

[Kim]

hey lucy ! so i don't think this would exactly be considered as an epistolary novel but I remember reading Life on the Refrigerator Door by Alice Kuipers a few years ago and it really touched me. probably not what you're really looking for but it's very quick and easy to read so you might want to give it a try :)
ps : the two POVS are a mother and her daughter