Wordless Wednesday: Mystery Burk-Mahler-Markell Celebration

These photos (scanned from negatives) were taken in the mid-1950s. My mother, baby sister, and we twins (shown above) are at a party where my father's Burk, Mahler, and Markell relatives are present.

I don't know who's who (except for Uncle Dave, at center of center photo below). Where are they celebrating, and why? Cousin Lois noticed birthday party things...whose birthday?

Update: Cousin Lois identified the couple above as Joan and Bob, with their son Andy.

Update: Above, the lady on the left is Lois's grandma, Ida. Below, lady on right is Ida's sister, Mary. Thank you for your sharp eyes, Lois!