Can an employer require evening social events/12-hour days at risk of being fired?

I work remotely for an online school. The employer has decided on short notice that we will be required to travel for 4 days to the home office for a "conference." (Travel was not in the original terms of employment.) We were told that having small children at home or being a single parent is "no excuse." We must attend or be fired. Once there, we're required to attend meetings beginning at 7:30 a.m. and stay through evening social events that are also "mandatory" until about 9 pm each day. Absence from these events has also been stated as grounds for termination. Can an employer require a salaried employee to attend evening events? These aren't meetings, just museum tours and receptions, but we have been told that any absence will result in termination. Thanks.