Te escribo porque querÃa saber cuándo van a venir a casa a comer un asado en familia, con mamá te esperamos con ansias. ¿Cómo andan mis sobrinas? Seguramente muy grandes. Bueno, estoy apurado, ya me tengo que ir al trabajo. Espero tu respuesta lo antes posible. Mucho amor, chau. A.
I'm writing because I wanted to know when you are coming over for a family barbecue. Mom and I look forward to having you here. How are my nieces doing? Grown up, of course. Well, I'm in a rush, it's time to go to work. I'm waiting for your answer as soon as possible. Lots of love, bye. A.
"Seguramente muy grandes" would be better translated as..."Grown up, I bet or I am sure" I really don't know what exact expression fits in there but, I think "of course" is not the corret one.