Ofcourse this ML was planned but I guess they had no fully prepared plan as they had no proof. They might have been just waiting for the right opportunity and figuring out the loop holes in Mrs k's plan. They themselve didn't have any idea what they would do next and hence had to pretend when they were alone too. Maybe acc to them it was the last chance to show that it wasn't shivaays baby. And also annika had to gain Tia 's confidence.
I must say billu ne khoob faida uthaya is fake ML ka. He made annika sleep in the same bed ( mauke pe chauka
đ). He knew that annika will not be able to do anything, though she tried very hard ( mujhe nahi lagta me aisi type ki ladki hu
đ). She couldn't fight with billu as annika na. But she is even more smart and did the pati parmeshwar drama to irritate billu ( tit for tat đ).
And then annika's investigation starts and she goes to gulmohar road all alone. Maybe that made shivaay angry and he got her back home as he might not have wanted her to land up in some problem alone. It's always shown that annika sometimes becomes over excited and in hurry to get things in front of everyone before being 100% sure which always lands her into some problem and shivaay didn't want that. Also annika doesn't know about the video. shivaay wanted nothing to spoil.
I think annikas banjh drama was only to irritate shivaay. And annikas sleep walk was a plan tabhi to billu time or bachane aa gayađ. And then Mrs K came up with some papers which could have bought serious problems in their plan. So shivaay decided to leave coz he has not signed the divorce papers and mrs k might then come to know about it and the video problem. But acc to annika divorce is gonna happen so she might not want to leave and thought this is the last chance they have and tells shivaay to marry Tia. ( that might not be a part of this plan )this makes shivaay very angry and also the fact that she told everyone that they were leaving. He can never marry tia coz usse pata hai divorce to kabhi nahi hua. Annika does not understand why is he against it and asks all the questions ( indirectly). And shivaay also asks indirectly ki usse koi ehsaas yaad nahi ( directly nahi bol sakte na). He was asking annika ki she has no feelings for him and she was ok if he gets married to tia ( thats what pinched him coz it was annika and not kalawati ). Also this wedding thing would have been a risk na. What if they don't find anything. That's why they did all ceremonies I guess.
And most importantly tha fark thing was also real according to me. Otherwise why would shivaay play this game with kalawati who doesn't remember anything. And the Rohit thing also makes sense coz it was annika but poor billu couldn't ask more kyunki they had to still pretend na ( tit for tat again). Also billu smartly used this to get the video jiske baare me sirf usse hi pata hai. And the song and feelings were all real. He wanted annika to say fark padta hai warna obviously kisi bhi wife ko fark to padega na. And that's why he is angry with annika.
And jaha tak kal ke thank you wale scene ka sawal hai I think annika plans to leave OM after all this and probably shivaay knows about it which makes him more angry ( why would kalawathi thank shivaay ). I am not sure about this though.
So finally this is all what I feel ( and hopefully what the cvs wanted to showđ) regarding all this fake ML. I think the best thing is to just wait and watch coz that's all we can do now.