How does 外国人にも出てもらおうと考えて work here

Question

For full context: http://www3.nhk.or.jp/news/easy/k10011281951000/k10011281951000.html

The sentence in question:

文京区は、新しい成人をお祝いする成人式に外国人にも出てもらおうと考えて、やさしい日本語と英語で書いた手紙を送りました。

My attempt at translation:

"Concerning the Bunkyo Civic center, considering to get the foreigners to come to come-of-age ceremony, where one gives gifts to the new adults, one sent letters which one has written in friendly english and japanese."

First, I hope I translated the intentional form もらおう here correctly. Im also not sure wether I interpreted the second meaning for もらう correctly here http://jisho.org/search/morau.

My main issue here is 成人式に外国人に. I think 成人式に expresses a direction here in relation to the verb 出る for which I used the meaning "to come to". 外国人に is a bit harder for me, since
A) I'm not sure what particle もらう demands when it has the meaning "to get someone to do something".
B) I am always a bit confused when a complex block of verbal expressions basically acts on two nouns. Syntactically, I think 外国人 must be the object of the predicative 出てもらおうと考えて, and would probably be categorized as an adverbial with local information. But I'm not sure, since I think that the verb 出る in the meaning "to come to" definitely requires an object, which would be 成人式. If thats true then the verbal expression 成人式に出る would be nested into the verbal expression 外国人にもらおうと考えて which itself required a verb (here 出る) to have the meaning "to get someone to do something". All these relations really make me skeptic of my interpretation, since I dont really know how to understand whats going on and therefore I cant be sure that I got it right ^^

Answer 1

I think you understand the meaning of もらう correctly: "to get someone to do~~". You also understand the relation of 成人式に and 出る correctly: "to come to the ceremony".

成人式に marks the direction (or the indirect object) of the verb 出る (≂ 出席する), "attend the ceremony."

「(人)に～～してもらう」 means "to get/have someone (to) do~~", so 外国人にも出てもらう means "to get foreigners to attend as well (as Japanese)".

文京区は、「新しい成人をお祝いする成人式に外国人にも出てもらおう」と考えて、やさしい日本語と英語で書いた手紙を送りました。

So the sentence roughly means:

lit. Bunkyo Ward thought "Let's get foreigners as well to attend the coming-of-age ceremony where we congratulate new adults", and sent letters that they had written in simple Japanese and English.

→ "Bunkyo Ward sent letters written in simple Japanese and English, hoping that foreigners would also attend the coming-of-age ceremony for congratulating new adults."

The (～を)お祝いする means "celebrate/congratulate", and やさしい here means "simple/easy" (≂ [易]{やさ}しい, not [優]{やさ}しい).