OET interlinear 1 KI 13:12

uW Translation Notes:

Note 1 topic: figures-of-speech / explicit

וַ⁠יִּרְא֣וּ בָנָ֗י⁠ו אֶת־הַ⁠דֶּ֨רֶךְ֙ אֲשֶׁ֤ר הָלַךְ֙ אִ֣ישׁ הָ⁠אֱלֹהִ֔ים אֲשֶׁר־בָּ֖א מִ⁠יהוּדָֽה

(Some words not found in UHB: and=he/it_spoke to,them father_of,their where? this [is]_the,way go and=they_saw sons_of,his DOM the,way which/who gone (a)_man the=ʼElohīm which/who he/it_came from,Judah )

By his sons had seen the road, the author means that his sons had watched the man of God leave and had seen which road he took when he departed from Bethel. As a result, they were able to tell this information to their father. You could indicate this explicitly in your translation if that would be helpful to your readers. Alternate translation: [Now his sons had seen the road that the man of God had walked who had come from Judah, so they were able to tell him]