That is one of the things wrong with Endeavor, that things are so miserable with the Thursday family.
The daughter was caught up in a bank raid ( along with Morse) and was apparently so traumatised by it that she left her loving family without a word of where she was going ( out of character) settled somewhere in the Midlands and had an affair with a married man.
Thursday then found out and visited her and secretly threatened the man ( looked as if her lover had hit her, as well.)
The son is in the army, and he seems to be distant with his Father as well, after being very close up to then ( again, why?)So Thursday has become very morose.To me, it seems all out of character, simply that the writers want to create tension.