"兼管数个教堂者" can be translated into English as "one who oversees or administers multiple churches" or, more concisely, "a person in charge of several churches".
If you're looking for a term that specifically denotes a clerical role, you might also consider "ecclesiastical administrator of multiple parishes" (though this is more formal and specific to certain denominations), or in a more general context, "a minister or priest overseeing several churches".
For a simpler and more commonly used expression, "a person in charge of multiple churches" is perfectly adequate.