OWD - Controls Record Access. Sharing Rule - Controls Record Level Access. Profile - Object Level Access
According to your first question, no the user cannot edit the records for other user ( sharing rule will not be created, will give an error that profile is read only) . However they can see each others record.
See Link : http://salesforce.stackexchange.com/questions/60656/profile-permissions-v-s-org-wide-defaults
Coming to your second question :
Profile works on object and OWD on record ( they are two different things ). It won't be a good idea to say that profile over rides OWD. But yes, Profile level permisson have a high preference, hence Profile permission will stand.
Consider a case where OWD - Private Profile - Read /Write In this case he users will not be able to edit each others record due to OWD being private.
However, in your scenario due to profile access being Read Only users cannot edit each others data.
OWD - Controls Record Access.
Sharing Rule - Controls Record Level Access.
Profile - Object Level Access
According to your first question, no the user cannot edit the records for other user ( sharing rule will not be created, will give an error that profile is read only) . However they can see each others record.
See Link : http://salesforce.stackexchange.com/questions/60656/profile-permissions-v-s-org-wide-defaults
Coming to your second question :
Profile works on object and OWD on record ( they are two different things ).
It won't be a good idea to say that profile over rides OWD. But yes, Profile level permisson have a high preference, hence Profile permission will stand.
Consider a case where
OWD - Private
Profile - Read /Write
In this case he users will not be able to edit each others record due to OWD being private.
However, in your scenario due to profile access being Read Only users cannot edit each others data.
Mark as solved if it helps.
Regards
Sreenath