Arianne Alive in the Stormlands, raises troops for claim on Dorne.
Jon has an event to give Sansa land
LF Events to seize the Vale from Robert, Robert can fight against it(AI should never fight it), Fighting means Arryn has an 80% of getting LF through the Moon Door
LF and Sansa's made friends(mostly for an easy scope to her)
Once LF is Vale Lord, he can seduce Sansa, Sansa can accept or reject, if she accepts she marries and joins LF(this is either going to his court if she is unlanded or switching liege to him), Jon is informed of it if shes accepts which he can accept or, if Sansa is landed, he can start a war with her over the North.
Vale Alliance, if Jon is at war, Petyr can make an offer to Sansa to join it, which gives him a favor on Sansa and Jon. Ai should always do this.