Can the Feast of the Holy Family Vigil Mass be celebrated on the evening of Christmas? Or are only Christmas Masses allowed on Christmas Day?
This year (2004) the Feast of the Holy Family will be observed on December 26. That does mean that the vigil will fall on December 25. I am not aware of a mandate that Masses on December 25 must be Christmas observance Masses; but, as the Feast of the Holy Family is not a holy day of obligation while Christmas is, individual churches may well decide to forego having a vigil Mass for the feast.
I suggest calling your local diocese to find out if there are any diocesan directives on the celebration of the feast this year.