I'm sorry for your pain at this time, GAG. You were there as such a wonderful friend and support to XMIL and to XSIL and XH.

Ask XH if it's alright for you to attend the funeral as a courtesy but know in your heart that it is your rightful place. As the others have said it's really about your relationship with XMIL, not your relationship with anyone else.

Take care,

Cas