The people of the parish of St. Rosalia (founded in 1902 as an Italian national parish, not a territorial parish) made a vow in 1942 to build a votive shrine, the magnificent Regina Pacis church, if their servicemen came home safe from the war and peace was established. In broad summary, that seems to be why this parish has two names. The history of the votive shrine from 1942 onward is given on the parish website. I have been unable to learn the parish history for the first forty years, especially whether there was more than one building for Sunday worship. This is not a merged parish. It is a parish that took on a supplementary name.
Some Catholic parishes with beautiful churches do not host weddings of couples who are not active attendees of the parish itself. The Regina Pacis website implies a ready willingness to assist the celebration of Catholic marriage.
A helpful reader pointed out that the parish also included St. Theresa's Chapel on 12th Avenue at 66th Street. A link to the news article with that information is HERE. Father Angelo Rafael Cioffi became pastor in 1923 and purchased the land for the school, chapel, and new rectory two blocks west of St. Rosalia's church. In the mid-twentieth century, Sunday Mass attendance was much higher than today, and pastors often had to add more worship spaces, churches, and chapels. I am guessing that in 1950, Mass was celebrated in three or four locations, the old church on 14th Avenue, the new shrine church upstairs, the same church downstairs, and maybe at St. Theresa's chapel. It would be interesting to see a Sunday bulletin or Mass schedule for that era.
The same helpful reader showed me this link to a website about church organs. The address given for St. Theresa's chapel appears to be in error.