he is deluded about his mother after she killed herself. from his own words prior to her death, natalia was messy and had previous run-ins with drugs/alcohol and her drunk dialing/texting him. it is easier for him to blame sonny and want revenge rather than deal with his feelings of guilt for shutting her out before she died and blaming her for her choices that led to her death
for his dad, he can't see that sidwell has manipulated him during his grief/pain after natalia died to draw him closer to the business with promises of revenge on sonny. he is also deluded thinking that sidwell won't go after lucas if he wants to go the authorities and reveal something is going on at wyndemere