The informants or declarants on a death record may have been relatives or neighbors of the deceased. Sometimes their exact relationship to the deceased is given in the record such as being a son or brother in law of the deceased, etc, but more often their relationship to the deceased is not stated in the record. You may, however, find that the informants were living on the same street as the deceased, if street names are given in the record for all parties involved.
As to witnesses in marriage records though, unlike in death records, you will find that they are individuals who personally know the groom and bride. Often a marriage record will indicate that the witnesses were produced by the groom or bride or both of them.
I agree with T about the child being 1 month and the mother's last name being Erme. I am looking at a current street map of the town and don't see any street name which is close to what the handwriting suggests. The street may have been renamed and therefore not appear on a current map.
I do see via Garibaldi on a current street map for the town, so it is a possibility. You're right though, T, the g is definitely different than the other one. I also think the d is different from the one in contadina, but I do think that the third letter which looks like an n could be an ri as in Patrica, but in the town name you see the dot over the i and I don't see a dot over the one in Garibaldi if, in fact, the third letter is not an n but an r followed by an i.