Estreature of bond means if he was originally arrested and bonded out, they will take that bond back in that the money posted by him or a bondsman will be forfeited and many times a capias (warrant) is also issued for his arrest. If it was through a bondsman, they will then be looking for him. It doesn't make sense that the date would fall on a Sunday. You should call the Clerk of Court ASAP to figure out actual date and if he can't be there he should definitely advise them ahead of time in writing or have an attorney handle it. Many times when an attorney is handling the case, a person's appearance can be waived.
This means that at some time in the past, your uncle told an officer, or a clerk, that his address was the same as your mother's. Call the bailbond company and tell them the situation...they may very well have another address for your uncle. If he does not go to court, his bond will be given to the clerk of the court, his license will be suspended, and a warrant (capias) will be issued. If you don't want that to happen give your uncle the letters and let him figure out when the court date is. Also, if you do not know who the bond company is, you can call the clerk and they will have the information for you.