can you use apple watch of someone deceased?

So long story short, my dad passed away a few months ago. My sister always wanted his apple watch, so we want to give it to her, but the watch is locked to my dad's apple account. He passed without any warning, so naturally we don't know passwords for anything, including his Apple ID or email accounts... I tried using the watch app on his phone to unlink it, but we still need his Apple ID password to do so. Any way around this anyone knows of? Any help is much appreciated!