Hey there, Brenda! Thanks so much for taking the time to stop by planDisney with your question. We appreciate it!
There is a Main Entrance Ticket Booth located between the Esplanade of the two parks and the Downtown Disney District that is open for in-person ticket sales. However, if you make an in-person purchase you still also need a
theme park ticket reservation. This means there's no advantage or special availability with in-person ticket sales. The reservation system is fluid and so there is a chance that more reservations could open up. I suggest you just keep checking the
Theme Park Reservation Availability Calendar and if you see reservations open up, grab them immediately! I've been able to get reservations for booked dates the night before a couple of times, so be sure to especially check then.
I know it's a real bummer if some of your family is not able to get into the parks for your mom's birthday. Maybe you could find a location outside of the parks for everyone to meet and celebrate if they aren't successful in getting reservations. Disney's Grand Californian Resort & Spa has a beautiful lobby that is a great place to take a break from the parks and Downtown Disney District has lots of options for a meal outside of the parks.
Brenda, I am hoping that some Disney magic happens for you and that your family members are able to get some last-minute tickets. Thanks again for stopping by!
Carrie