1)should i let Nicki play with this dog or not i.e. will nicki learn da dogs bad behaviour or not.
As mentioned, Nicki will learn a lot from your other dog, both good stuff and bad stuff. As a pup, I would limit his interactions with your older pup to one or two hours per day (you don't have to, but that is what I would do if Nicki was my pup). You want Nicki to bond to you and think of you as the main play-mate in the house. Often when a pup spends all his time with another dog, he bonds to the other dog so much, they stop paying attention to humans at all, and then future training is a challenge.
At the same time learning how to interact with other dogs is very important also. So yes, I would allow Nicki so time to play with your other dog, but not a lot.
2)They usually lick each others mouth and i would like to ask is it harmful or bad?
No, this is a normal. They are telling each other that they like each other, and are showing that they will submit and not challenge them. Nicki is doing it to show the older dog that he accepts his dominant status over him, and the older dog is doing it to let Nicki know that he likes him, and will be his friend.
3)Nicki has begun Jumping on me and people what should i do?
Teach him to sit when greeting people. Give people treats to give to Nicki when Nicki sits for them.
4) Should i keep Nicki in a crate for some time or i can still play with him
The more you play with him, the better! As mentioned, this will help develop a strong bond with him. He will still need to be crated at night, for house-breaking training, and whenever you don't have time to supervise him. For his mental and physical development, the more he can be out and about (supervised!!), the better.
5)Can I keep Nicki in a crate for long hours since i am a very busy person please?
In general, puppies can "hold it" for an hour for every month of their age, plus one.
So a two month old puppy can be crated for three hours max without a potty break (exept at night, many will start sleeping through the night at that age).
A three month old puppy can be crated and expected to "hold it" for four hours, and so on.
But as a young puppy, I would work around not having the puppy spending a lot of time during the day in the crate. If you are very busy, you still need to find the time and arrange your schedule to make sure Nicki's mental and physical needs are met. So when you are home, make sure he gets a lot of play and exercise time.
By the time the pup is six or seven months old, they should be okay crated during the day without a break if you have to work and cannot make other arrangements.