Hello.. I also had a problem of mouse getting in..
First you have to stop acceess to the place just under the windshield.
I think they get in there through the water outlet. Then it can go into the hole whare the fresh air get inside. You may cover those 2 holes by using a metel net which have drills that do not allow the troble makers to go in.
To see inside clearly you have to remove the plastic grill. It is not a difficult job.
Remove the caps of the wipers at the root by just pulling it out
And remove the wipers by loosoning the nuts. You may need to fold the wipers out side to remove them easily.
open the bonet. There are 4 clips and 2 plastic bolts. Remove them carefully.
Then you can remove the enitere plastic grill. But it has tubes connected with wires going to the mortor. So you may keep it little away and see inside.
Now you know how to get in there rather than through doors or windows..