A question about birds

Hi,

Swallows have nested in my barn for many years now, they always use the same nest.

Last year they had one chick then later a second clutch of two. The five of them hung around until it was time to go. This year they are back but this time there is three adults using the nest! Is this unusual? Could one of them be the youngster from last year? I just thought it's strange but maybe you will say different. They all fly around together during the day, aat night the three of them share the nest but there is a lot of tail feathers over the edge!