was the shastri also helping shyama in getting ranga married to ratna?

Yes. From instances in the story it is quite clear that Shyama had pursuaded Shastri to talk about Ratna while foretelling Ranga's reason for staying upset. When Ranga and Shyama arrived, Shastri told accordingly that Ranga's stars were in favour of a girl, someone with a name which meant something that was found in the ocean. All this clearly showed Shastri helping Ranga to dwell upon the thought of being with Ratna.