How can I cancel/end process1 from process2 if I have the processID for process1

You can try a Send Message node inside of process1 and a Receive Message node inside of process2:

forum.appian.com/.../Send_Message_Event.html
forum.appian.com/.../Receive_Message_Event.html

For the Send Message Event setup in process2, the JMS Message Destination will be process and the Message Type will be Process to Process. For the data, you will add a mapping on the Data tab too target the ID for process1.

For the Receive Message Event setup, the message type will also be Process to Process. This Receive Message node will be detached from the main process model but will flow directly into a Terminate Process node (search for Terminate Process Trigger inside forum.appian.com/.../End_Event.html) to end the process regardless if all end nodes of process1 have been met.

You can try a Send Message node inside of process1 and a Receive Message node inside of process2:

forum.appian.com/.../Send_Message_Event.html
forum.appian.com/.../Receive_Message_Event.html

For the Send Message Event setup in process2, the JMS Message Destination will be process and the Message Type will be Process to Process. For the data, you will add a mapping on the Data tab too target the ID for process1.

For the Receive Message Event setup, the message type will also be Process to Process. This Receive Message node will be detached from the main process model but will flow directly into a Terminate Process node (search for Terminate Process Trigger inside forum.appian.com/.../End_Event.html) to end the process regardless if all end nodes of process1 have been met.