Translation:Would you live at František's parents'?
duolingo's handling of plural possessives is notoriously suboptimal. the grading algorithm performs string substitutions when comparing the user's answer with the list of accepted answers. one of those substitutions apparently strips the required word-terminal apostrophe from the accepted answers to expand that list in an effort to be more lenient. unfortunately, the exectution of this maneuver is not without errors and produces confusion in discussion headings and in correction messages to users.
it also makes it seem as if the volunteer teams do not know what they are doing, while the fault is with the professionals in pittsburgh who take correctly configured content and manage to turn it into incorrect messaging.
There is no way it could give you parents without the apostrophe unless there is some serious bug in the Duolingo system. Sorry, you really, really confused me, but in the morning there was not a single accepted variant without the apostrophe. I only added it later because I thought you are requesting it (and I thought it is correct myself).