Talk to son and see how he would feel if he house-sits without you. Also, he may be very understanding to you wanting to go to Seattle. If its OK with him, then go ahead and make arrangements to go to Seattle.
If son is not OK with a change in plans, then I feel you need to follow thru with your prior commitment. This is the part of DBing where you need to choose which principals you're gonna live by and how they affect all others around you.
