If I borrowed money from someone, and he died before I paid him back, (in a situation where I now owe the debt to the children of the deceased lender), may I name my child after him, or, since not only money, but anything given to the lender in addition to the debt principal is considered Ribbis, [see HERE], and since the children will feel honored that I gave the name after their father, would this honor be considered paying ribbis, interest, to the children whom I now owe the debt to?
The Kitzur Shulchan Aruch (65:9-10) seems to say pretty clearly that anything that is an honor to the lender (that you wouldn't have done if not for the loan) is in violation of Ribbis (quoting the most relevant bit below):
אִם לֹא הָיָה הַלֹּוֶה רָגִיל לְהַקְדִּים לְהַמַּלְוֵה שָׁלוֹם בְּפַעַם אַחֶרֶת, אָסוּר לְהַקְדִּים לוֹ, וְאָסוּר לְכַבְּדוֹ בְּאֵיזֶה כִּבּוּד בְּבֵית הַכְּנֶסֶת אוֹ בְּמָקוֹם אַחֵר, אִם לֹא הָיָה רָגִיל כֵּן גַּם בְּפַעַם אַחֶרֶת. וְכֵן שְׁאָר רִבִּית דְּבָרִים בְּעָלְמָא אָסוּר, שֶׁנֶּאֱמַר נֶשֶׁךְ כָּל דָּבָר אֲשֶׁר יִשָׁךְ, אֲפִלּוּ דִּבּוּר אָסוּר.
If it was not the usual practice of the borrower to initiate greetings to the lender on other occasions he may not initiate them [now]. [The borrower] may not honor him with any sort of honor in the synagogue or any other place if it was not his usual practice to do so on other occasions. So, too, other types of ribis of words are prohibited, for it is said "Interest of any thing which is interest." [The sages interpret this to include] that even verbal ribis is prohibited.
It seems fairly straightforward to me that this would apply to naming a child after someone related to the lender. If this is something that would be an honor for the lender and it's something you wouldn't have done otherwise, it would be Ribbis.
If you would have named your child after the person even without the loan (i.e. the person who passed away is your family member too), it would not be Ribbis. Additionally, if this could be construed as something that wouldn't be an 'honor' for the lender (which admittedly is very subjective, although most people would likely consider this an honor), then it would be permitted as well.