On 22 July 2012, I went with my grandparents in Tunisia
On the 22nd of July 2012, I and my grandparents went to Tunisia. Ou garde ta structure mais GO TO, pas GO IN
I go every year in the same hotel (the Hotel Mahdia Palace) since I was a kid.
Since I was a kid, I've been going every year to the same hotel.
(since -> have-en ou have been vb-ing)
We were at the airport at 11 am and we boarded at 13:30.
I was sitting on the seat C432, side window.
I sat in the C432 seat, which was a window seat.
What luck, I love to watch the scenery!
What luck did I have! I must admit that I love watching the landscapes from above the clouds.
Moreover, I've always loved traveling by plane ... except one.
except ONCE, when I had a very bad experience.
After 1 hour of flight, there was a huge storm! All the lights suddenly went off, the passenger were panicking, they cried!
the passengerS panicked (concordance des temps)
The plane was shaking and the oxygen masks have fallen.
There were turbulences and the oxygen masks were released from their compartments.
Finally, we went down to Rome airport to wait out the storm.
The captain then decided to land at the Rome Airport to wait for the storm to get over.
We left the next morning at 8 am. I wouldn’t like to go through that again ! Fortunately, the airline has offered free return ticket.
the airline offered free return ticketS
I doesn’t know if we will go in holidays next year, my grandparents were very upset and they get old.
I DON'T know WHETHER we'll go ON holiday next year, as my grandparents got very upset. Needless to say that they are aging too...
Voila pour ton premier texte 
J'ai essayé de ne pas modifier le vocabulaire et les tournures de phrases de manière à ce que ce soit proche de ton texte original. Je suis un peu à la bourre donc j'ai pu manquer qqch ou faire une maladresse mais ça sera déjà mieux ;)
Cheers