Find conflicting lines and authors after merge

There is no such thing as "automatic merge". A merge conflict happens when two humans have made "incompatible" changes. A human must manually decide what changes to keep. The command to run is: git mergetool
This will bring up an editor highlighting the conflicts.

I also recommend setting up a gui to edit the changes. There are many options, this one is as good as any: Setting up and using Meld as your git difftool and mergetool - Stack Overflow[^]

A good way to reduce conflicts in the future is if all team members update their local branch AND merge as often as possible.

I am really sorry, the following may not be a resolution to your situation, but it what it seems like to me:

I think this is not exactly a technical question. It seems to me like an organizational one. It is a matter of "ways-of-working". Every programmer should find and resolve his own conflicts. It is totally unacceptable to burden one person [you] with other peoples unfinished work. They must learn to use git mergetool on their own conflicts.

I realise you may be up against a hard to convince group of programmers and maybe management. But this is what you should push for. Or... to find other tasks within the organization.

To communicate a conflict as filename:linenumber is extremely inefficient, when they could graphically see it on their own screens, automatically. And it will not be enough anyway, because somebody still has to choose between the changes from two different persons.