My daughter and her boyfriend signed a lease with another couple. The owner/Landlord is the mother of the male in the other couple. She is giving the house to her son and his girlfriend. Since the lease was signed with all 4 parties, and she is basically cancelling the lease with 2 of them. Does this not mean that my daughter and her boyfriend are no longer tied into the lease? Does this cancel the joint lease??

... the lease was signed with all 4 parties, and she is basically cancelling the lease with 2 of them. Does this not mean that my daughter and her boyfriend are no longer tied into the lease? Does this cancel the joint lease???

No. She has to have cause to cancel the lease. You have not indicated that she has any such cause. Each of the 4 lessees, including your daughter and your daughter's significant other, can refuse to let her cancel. The lease would continue for it's full term.