Issue with Users and Multisite Network

So here is the scenario-
Multisite on subfolders, no domain mapping.

We came across an issue today where a user that is currently registered on another site (SiteOne) on the network tried to login to another site on the network (SiteTwo). However, they forgot their password, so they tried to reset it on SiteTwo who they originally were NOT with. They were unable to retrieve their Forgot Password, because they were not originally registered on that site.
1) Is there a way for them to be able to retrieve their password without having to remember their original registration site AND without having to contact that particular site admin to manually allow them to join their network?
2) How do we edit the 'Joining confirmation' email for the network?