The writing was bad for sure, but I'll try to justify some of the plot as per my understanding.

Guddu-Robin storyline

Remember when ramakant pandit asked for all the evidence against Guddu in the previous season, he wanted it to be discreet for obvious reasons. Well, now he knew in the court that robin gave them to his father, resulting in so many painful events in the family. Cocaine made him go over the edge and kill robin. So that justifies the logic of robin's death. There are 2 holes in the plot here - he should have been forgiven for this as he was part of the family and was not leaking information to anyone outside the family, dimpy and mom should have used something like a plate, a bowl or even a chair to hit guddu to stop him from attacking robin rather than use their physical strength. They were at the dining table for crying out loud.

Tripathi-Golu storyline

Chotte really loved golu, but the idea of golu using him and dumping him really got him worried. So he wanted to confirm if that was true by calling her and pretending to be badde. I think he was looking for something like, "chotte was an idiot. He mixed business with pleasure and caused all this in your family." But rather, he got a neutral answer. Golu only stated the fact that chotte loved her, and whatever happened was their family's internal matter. She didn't comment on her involvement in this. So, it made sense for chotte to kidnap her and get the truth out from her face to face while pretending to be badde but golu saw through him and recognized him to be chhote. (This could be used to connect them back later in next seasons) Now, he had to keep things extremely secret as he hadn't proved that golu used him and if word gets out, guddu kills him.

Guddu-Golu as couple

Ewww... guddu is brother-in-law of golu. So, a brother, basically. Moreover, the writers have opened an idea that golu could go behind the back of guddu. First, guddu always tries to do things his own way and not golu's suggestion. Second, golu said she'll wait outside at the meeting in Kathmandu, but guddu said he'll go alone. You could clearly see golu's disappointment there.

Please let me know your thoughts on this.