Davening in shul vs. davening in an avel's home

Question

Two scenarios:

1 - A person has a choice of either being the 10th person for a minyan at either a shul or a mourner's home. Where should he go? Assume that one of these 2 places count on him to form the minyan. Without him, they won't get anyone else.

2 - A mourner cannot get a minyan at his home unless the minyan (consisting of exactly 10 people) from shul would all come to his home. Should these 10 people daven in the shul, or should they all form a minyan in the mourner's home?

These people cannot daven at both places because, I believe, there is a rule that at least 6 people should not have previously davened in order to be able to repeat the Amidah.
^{(Source: Kitzur S.A. סימן כ - דין חזרת תפלת השליח צבור)
אֵין אוֹמְרִים תְּפִלַּת שְׁמֹנֶה עֶשְׂרֵה בְּקוֹל, אֶלָּא אִם כֵּן יֵשׁ לְכָל הַפָּחוֹת שִׁשָּׁה אֲנָשִׁים, שֶׁהֵם רֹב מִנְיָן שֶׁהִתְפַּלְּלוּ עַתָּה.‏}

The main concern - Does davening in a shul have the highest priority? If so, why?

Answer 1

There is a concept of שלא לבטל התמיד - not to disrupt the continuity of a miyan. This is brought in the Ram"oh (55/22), where he writes that fines may be imposed in order to keep a steady minyan. The Mishneh Berurah (55/73) writes about people interrupting learning in order to keep the minyan in shul on a steady basis. It would seem that based on the above, the minyan in shul should be the one to go to. [As noted by Danny in his answer, the avel could/should also go to shul if possible.]

Answer 2

The Kitzur Shulchan Aruch says in סימן ריד - מתי האבל יכול לצאת מביתו says that they should all go to shul - including the mourners - if there cannot gather a Minyan in the mourner's house.

אֲפִלּוּ לְבֵית הַכְּנֶסֶת לְהִתְפַּלֵל, אֵינוֹ יוֹצֵא בְּתוֹךְ שִׁבְעָה, רַק בְּשַׁבָּת. אַךְ אִם אִי אֶפְשָׁר לֶאֱסוֹף עֲשָׂרָה וִיהֵא מֻכְרָח לְהִתְפַּלֵל בִּיחִידוּת וּבִשְׁכוּנָתוֹ יֵשׁ מִנְיָן, יָכוֹל לָצֵאת לָלֶכֶת לִהִתְפַּלֵל שָׁם, שֶׁלֹּא לְהִתְבַּטֵּל מִתְּפִלָּה בְּצִבּוּר‏