Is there any difference in meaning between the following sentences?
My understanding is that the pronoun "nos" indicates possession and there isn't any difference between both sentences. If that's indeed true, which sentence is more usual?
Between:
a) Se nos casó María.
and
b) Se casó nuestra María.
I can see at least three differences:
In (a) "nos" may indicate possession or interest. Maybe María is our friend, our sister, our daughter, and we are thus emotionally affected by her marriage. This emotional involvement is not necesssarily present in (b).
"nuestra María" may be used to indicate that there is more than one María, and it is ours (the one we know, the one who is related to us) that got married. As the possibility of there being more than one María is more limited, so is this use.
Both sentences are rather colloquial, but (b) is more so because it can be associated with the very colloquial use of articles before proper nouns: Se casó nuestra María could thus be equated to Se nos casó la María.
Rather than focusing on the grammar, I'll focus on the practical meaning, and the feelings behind these sentences.
We might feel somewhat abandoned. Comparable: She up and got married on us.
This focuses on our affectionate feelings toward her. Comparable: Our dear Maria got married, Darling Maria got married, or Our Maria got married. In UK English I've heard "our" used this way.
They express slightly different feelings and attitudes about the event.
I guess "Se casó nuestra María" might be less common -- perhaps it's a tiny bit awkward sounding.
