В Present Continuous смысловой глагол приобретает окончание -ing. Вспомогательный глагол to be ставится в нужной форме (am, is, are) в зависимости от подлежащего.
Dear Sara,
How are you? I am having a great time here in Spain. My family is with me. My mom is cooking delicious food, and my dad is reading a book. My sister is playing in the garden. I am enjoying the warm weather and the beautiful scenery. How is everything with you?
See you soon!
Love,
[Your Name]