You mentioned a while back that your parents have been difficult. In light of this, please be very, very careful tonight.
Your mother's initial response on the phone this morning was probably subdued because she was shocked by the news, but by the time you get home she'll have had a couple of hours to stew over it. I can almost guarantee that she has already told your dad so that she can get him to back her up.
I hope I'm wrong and that it all goes swimmingly. But please be prepared for the possibility that they might gang up on you. If you can, call a friend or relative nearby and make a contingency plan to stay round their house tonight, just in case. That way, if things go badly with your folks, you can just walk out of the door and put some space between you so that everyone can calm down. And whilst I don't want to over-dramatise what might happen, never be afraid to call the police if you think your safety is at risk.
Above all else, take care of yourself.