Sure! Here are the verbs in brackets filled in with the correct form:

Hi Marvin,

1) I **'m writing** (write) this letter from Portugal. I
2) **am** (be) on holiday here with my family and we
3) **are having** (have) a great time.

Right now, I
4) **am lying** (lie) on the beach. My little brother
5) **is playing** (play) on the sand with his toys and my mother
6) **is watching** (watch) him. My dad
7) **swims** (swim) in the sea.

I just love it here. We
8) **get up** (get up) late every day and
9) **spend** (spend) most of our time sunbathing.

This afternoon we
10) **are going** (go) into town to do a little sightseeing. Then my parents
11) **are taking** (take) us to a nice restaurant. They
12) **want** (want) us to try the local cuisine. I hope it tastes good!

Well, that’s all for now. See you when I get back!

Take care,
Wendy