My uncle passed away and not able to login into his ipad

Contact Apple. 

How to request access to a deceased family member's Apple accounts - Apple Support.    *

Apple ID - Official Apple Support.   -

Contact Apple for help with Apple ID account security - Apple Support.  *  (Link doesn’t always load)   

Get Support    -  Work through the screens to get a chat option. 

Apple Support schedule phone call.  -

Apple on Twitter-  

Sorry for the loss.

See -> How to request access to a deceased family member's Apple account

How to request access to a deceased family member's Apple account - Apple Support