Can I get full custody of my 3 kids when the father has not followed the parenting plan for over a year?

There is no "full custody" in WA, only residential time and decision making authority. You have them the majority of time. If the father isn't using his time, the kids are with you full time. If you have joint decision making and the father hasn't seen the kids for a year, you can make a petition for modification that gives you sole decision making authority and requires him to do certain things before he sees the kids again. It's likely not worth the cost of doing that.