Can someone explain I'm still confused how tf did that grandma knew those gangsters

We don't know for sure, but I assume that Grandma borrowed money to pay for Dan's college education. ╥﹏╥

i dont think so coz in one of the panels the gangsters appeared when he was a kid too

Yes! I had forgotten about that. Now I think the debt was inherited from Dan's parents, his dad? and this is the motive for the murder/suicide? It's a theory ╮(￣▽￣)╭