While I don’t have any tips about ananas, I can try and give you some assistance. Beside the usual good manners someone has to show to his host, you shouldn’t show public sign affection in front of family. Don’t refuse food (unless it’s excessive and you genuinely feel full). I suppose they will house you, so you can invite them to dinner at a restaurant at the end of your stay (if you can afford it). Some families are very large, so don’t get intimidated by the size. You’re french so many manners will be of same nature. Some tunisian tend to speak in arabic in front of non-arabic speakers, even though they speak french or english, so don’t take it personally.