How to make two childs get closer to each other?

Maybe stop calling her a princess, for starters. She's your daughter, full stop.

And you cannot make this happen. You can pay attention to your son and have special alone times with him. His world, after all, has been turned upside-down. But you cannot force them to care for each other. They either will, or they won't.

Set some alone time with him. And call it that. This is your special time with mommy/daddy or both. No baby.

He needs to know he is important. Put yourself in his place. You both were his whole world - he got all the attention. Then this little crinkly creature shows up. One that just sleeps, eats and poops. No fun for him. And to top it off you call her a princess and pay all your attention to her care. He is now left to himself and to top it off he is supposed to be all goo goo over this creature that has done nothing but cause him grief and change his world as he knows it.

4 year olds are very ego centric. Just their make up. His behavior under the circumstances is perfectly normal. But you can make it more pleasant and easier if you give him attention.

He will eventually care about her - once she is able to interact more with him and he will appreciate her more if he feels she has come and destroyed his life as he knew it. That mommy and daddy still shower affection and attention to him.

Yaa this actually making us detached with elder one. He questions a lot why only little one is allowed to sleep with mom. And why does she feeds only the new born. Though I am trying to convince him, and explain the facts. But it is taking time.

Why in the world would this make you detached from the older one?

Who's the adult here?

Wait a minute, adults. You say both of you are detaching. Seriously?

Two adults are detaching themselves from a 4 year old because his world has been turned upside down? Because he's asking questions so that he can make some sense of it all? To want reassurance that his mother and father still care for and will take care of him?

Your son has a job, being your kid. It's all he knows.
If you or your husband showed up at work, and some stranger was sitting at your desk, demanding and getting all the attention from co-workers, superiors and even complete strangers, I guess you'd be asking what was going on, and be pretty worried you no longer have a place.