What is {relative} of {Peter} that is {type of kinship} is {mother-in-law} ?
Who is Peter's spouse's mother?
Who is Peter's mother-in-law?
SELECT ?w WHERE { resource:Peter property:relative ?x . ?x property:kinship_to_subject resource:mother-in-law . ?x property:relative ?w }
select distinct ?obj  where {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q33923> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P1038> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> ?obj .
?statement <http://www.wikidata.org/entity/P1039> <http://wikidata.dbpedia.org/resource/Q723868>
} 

SELECT ?obj WHERE { wd:Q33923 p:P1038 ?s . ?s ps:P1038 ?obj . ?s pq:P1039 wd:Q723868 }