Which present day city in Algeria, founded by the Roman emperor Trajan around CE 100, was named in commemoration of his family members - mother Marcia, eldest sister Ulpia Marciana, and father Marcus Ulpius Traianus?

The city in modern-day Algeria is called 'Timgad'. It was founded in the Roman province of Mauretania by the Emperor Trajan in AD 100 and named after members of his family. Its full and proper name is Colonia Marciana Ulpia Traiana Thamugadi. The last name is from the Berber language and means 'summit' or 'peak'. That explains its modern name, 'Timgad'. Substantial ruins remain which show the elaborate grid-plan that underlay Roman cities. See https://en.wikipedia.org/wiki/Timgad.

See also https://arxiv.org/abs/1903.10314 for the information that the city was oriented toward the rising sun on Trajan's birthday, 18 September.