I just quickly ran it though a Japanese dictionary/name database:
慶 is jubilation,congratulate,rejoice,be happy and the name database has many ways to say it and yes 'yoshi' is a popular one of them ('kei' also seems popular)
身 is somebody,person,one's station in life and looking in the names database seems to usually be said 'mi'
However I don't see them listed together (慶身) at all. What that means is that it's certainly possible for 慶身 to be said Yoshimi but it would be extremely unusual.