Are these sentences correct:
“1. He has his car repaired twice a year.
2. We had many photos taken yesterday.
3. She had her car stolen two hours ago.” ?
Thank you for your time!

I am sure that everyone would correctly understand numbers 2 and 3.

But – in theory – they could be ambiguous.

No. 2 could mean that some bad people broke into your house and took many of your photos.

No. 3 could mean that she told some bad guys to steal her car. (Insurance fraud)

So, in order to avoid any confusion, I would say:

We took a lot of photos yesterday.

Her car was stolen two hours ago.

Of course, in real life your sentences are fine. Everything depends on context.

Thank you, James M for your explanations but I noticed that the causative form is : have/get + d. object + past participle; so, it’s not about ‘We took a lot of photos yesterday.’ , somebody else took these photos for us and in this case we use passive because I intend use 2 sentences: -one with the active voice: A.V. : He repairs his car twice a year.( he repaired his car on his own without any help)
-the 2nd with the passive : P.V.: He has his car repaired twice a year. ( he let his car to a service garage so that the mechanics should repair it for him)
No. 3 couldn’t be used with the active, you are right!

Thank you, Antonella, for your note.

I am sure one of the language coaches will soon answer you.

original sentencews 2 and 3 are correct.
1 is a little strange. I would suggest ‘serviced’ instead of ‘repaired’. A car is only repaired if something breaks. There is no guarantee that somethin on a car will break twice a year every year. Apart from that vocabulary choice, the rest of the sentence structure is okay.