Catholic folks I am lost about saints?

I asked before but I don't get is that true there is a saint for each thing, for specific purpose, like the saint of the impossible like saint jude or any marian devotion.. for example I learn our lady of the sacred heart was for impossible things like saint jude, Our Mother of the Mount Carmel was the Patron of the Mount Carmel and she is the Queen of Purgatory.. many people put her picture during a funeral or novena for the dead people.. I love this devotion but I also I like our lady of the perpetual help but it's the same mary but under different ways.. and I have faith in many saints but I feel bad to ask one saint and another saint at the same time.. also to pray to mary under two advocations.. please help me thanks.