My father is at his wits end as well. Sometimes when we have difficult relationships, we allow our indecision to make the decisions for us. Perhaps when you 'warn' your mother you won't be there for a holiday, you know she will act out, and that gives you the excuse to spend the holiday with your husband's family. Behavioral therapists would term this either 'learned helplessness' or simply 'helplessness'. It appears that this particular issue would be very amenable to some counseling.
Passivity is often a catalyst to further destroy relationships.
Don't let what you've learned in the past affect your present relationships. Work on this, you can overcome this old pattern with some insight and some support of you making and sticking to clear decisions. Nancy Brooks is a psychotherapist in private practice in Denver.