I'm surprised the funeral director didn't assist with forming the line or ask you, (wife & children) or his siblings about who should or would like to be in the line.
In our family, siblings of the deceased stand in the receiving line. Closest to the casket is the spouse, followed by oldest child, (or oldest child nearest the casket, if no spouse) and other children according to birth order, which includes their spouse, if married. Then the siblings of the deceased. Grandchildren are welcome, too.
If the family is quite large, I have also seen spouse and children on one side of the casket and siblings on the other.
I am sorry for the loss of your father. I don't think you did anything wrong. Considering how many decisions need to be made when a loved one passes, it's a wonder that everything gets done at all during such a difficult time.
If his siblings are elderly, they might have expected it to be handled in a "formal" or certain way. If they are important to you, perhaps you could clear the air by explaining the oversight was not intentional.