"兼管数个教堂者" can be translated into English as "one who oversees or manages multiple churches simultaneously" or, more concisely, "a person in charge of several churches".
If you're looking for a term that specifically denotes a cleric or religious leader with this responsibility, you might use "a multi-parish priest/minister" (though "parish" typically refers to a specific geographical area served by a church, the idea of overseeing multiple can be adapted in context), or more generally, "a religious leader overseeing multiple churches".
For a more formal or official-sounding term, "ecclesiastical administrator of multiple churches" could also be used, though it's somewhat technical.
In everyday conversation, the simplest and most straightforward translation would likely be "a person in charge of several churches".