Respect of parents (kindness to them) is excepted only when it would lead to shirk:
And We have enjoined upon man goodness to parents. But if they
endeavor to make you associate with Me that of which you have no
knowledge, do not obey them. To Me is your return, and I will inform
you about what you used to do. 29:8
Furthermore, there is nothing in the Quran about obedience to parents, in fact it states very plainly that in the face of justice, stand firm:
O you who have believed, be persistently standing firm in justice,
witnesses for Allah , even if it be against yourselves or parents and
relatives. Whether one is rich or poor, Allah is more worthy of both.
So follow not [personal] inclination, lest you not be just. And if you
distort [your testimony] or refuse [to give it], then indeed Allah is
ever, with what you do, Acquainted. 4:135
Obedience is only for Allah, not for parents; and finally:
And your Lord has decreed that you not worship except Him, and to
parents, good treatment. Whether one or both of them reach old age
[while] with you, say not to them [so much as], "uff," and do not
repel them but speak to them a noble word. 17:23
Keeping all the above in mind - I would recommend to avoid any confrontations and treat him with respect - as children are not the judge of their parents and the true judge is Allah.
May Allah grant them all patience and strength of will in this difficult time.
And Allah Knows Best.