Translation:We admired Kahless's father's sister's husband.
The various respected style guides disagree on how to do possessive in words that end in s. Some say if it ends in s just use '. Some say always use 's. Some say on a singular endings in s, use 's, but on a plural ending in s, just use '. We try to accept all of them and may be inconsistent in which we use for the "best" translation.
I think you will find that authorities disagree on whether, when the noun is a singular noun ending in -s, you should just put an apostrophe or an apostrophe and an s. If you do an internet search for the topic on grammar websites, I think you will find a majority opinion that the added s is proper. That is what the software is going to continue to show you in the Best Translation. However, it does seem that we failed to account for the also acceptable opinion that the extra s is not needed in the Accepted Translations. I have added that option for this sentence. If you come across any other sentences that don't accept just the apostrophe following a noun ending in -s, please use the report flag to notify us.