Welcome to Yorkie Talk!
I agree with everyone above that there will likely be a period of adjustment. Supervise the dogs closely to see how they are getting along with Jack Russell/Chi. Does he or she have experience with other dogs? All 4 will establish a pecking order, but do everything for your JR/Chi first to let him/her know that he/she is not being replaced. Greet first, put down food bowl first.
Establish a routine for doing all activities at about the same time each day. That will lay a foundation for you to teach your new doggies some manners.
Best wishes!