But the other two are not accepting to pay the extra amount not willing to break the lease .what should we do?? Please help...

The roommate who wants to leave must continue to pay rent until a suitable person can take his or her place as a subletter - just get another roommate.

You posted this question in the Small Claims forum for a reason.

Yes, all room-mates are jointly and severally liable for the entire amounts of the monthly lease payments, including the one who wants to leave.
And yes, if the one who wants to leave fails to pay his or her share, he or she can be sued in small claims court by the other room-mates.

Not that it matters, but your question was unclear as to how many room mates are on the lease.
In the title you said you signed with four roommates. That would be 5 in all.

But then you mention "the other two".

You,
plus the one who wants to leave,
plus an "other two" would be a total of 3 (if you are one of the "other two) or 4 (if you are not),
but wouldn't be 5.

Depends on how the lease is worded. But most likely it is worded that all roommates are responsible for the rent. So, if one doesn't pay, the others need to make up the slack or face eviction.

In such a case, the landlord doesn't care what is going on and will not go after the one roommate separately.

The roommate who wants to leave is breaking the lease. One can't just break a lease, it is a binding contract. So you find a replacement and tell the roommate who wants to leave they have to pay until you do find a replacement.

Yes assuming you are all jointly on the lease, if the one roommate leaves, the other ones will have to just pay up and pay the full amount of the lease. You may then ( the three of you) sue the ex room mate for the money.