Thank you very much. Here are some more sentences I'd like you to check.

I thought the sentence "In my family, we are in three" was incorrect.

1)I like doing a lot of things like hanging out with my friends, cooking with my mum and travelling with my friends.
2) I like playing football and volleyball with my nephews. I also like helping them with (their) homework. My other hobbies are playing the piano in the church (?) and playing the clarinet in the local band.
3) I like eating pizza, but I don’t like eating kiwi (?). I don’t like drinking milkshake (?), too.
4) I love spending time with people I care about and with people that make me laugh. I adore the summer, the summer rains and the long, sunny days. I hate waking up early. I also like (the) spiders and horror movies.
5) I play the clarinet in the local music (not musical) band and I take lessons of this instrument (better: clarinet lessons) in the music institute of my town once a week.

The comma after "family" is correct.

1. comma needed

2. "playing piano at church"

3. Better: I like pizza, but I don't like kiwi. I don't like milkshakes either.

4. "people who..." -- comma needed after "rains" -- delete "the" before "spiders"

5. delete "music" and "musical" -- comma after "band" -- "I take clarinet lessons"

Here are my suggestions for the sentences you provided:

1) The sentence "In my family, we are in three" should be revised to "In my family, there are three of us."
2) The sentence looks good, but you can add an article before "church" to make it "in the church" and you can remove the parentheses around "their" in "helping them with their homework."
3) The sentence is correct, but you can add an article before "milkshake" to make it "drinking a milkshake" or specify a particular milkshake like "drinking the milkshake I had yesterday."
4) The sentence is fine, but you can remove the articles before "spiders" and "horror movies" to make it "I also like spiders and horror movies."
5) The sentence is correct, but you can replace "music" with "musical" to make it "I play the clarinet in the local musical band and I take clarinet lessons at the music institute of my town once a week."

Overall, the sentences are well-written, and with these minor revisions, they will be even better.