The pattern 又。。又 means not only, but also or to put it even simpler, it means and. 他又聪明又He is not only clever he is also handsome/ He is clever and handsome. So in your example it says says festivals and weddings. 热闹 means lively, put 2 together it means to have a lively/fun time. 顿 is the measure word for meals and beatings-这顿饭-this meal.

Upstairs Beth did a very good job in question 2 and 3 in my opinion, but I do not think question 1 is exactly right. 1 又…又… means not only, but also in this sentence. "又过节又结婚，双喜临门。" For instance, one gets married in 25th December this year, and that day is the Christmas Day. He/She not only gets married, but also celebrates a festival.（他/她）又过节又结婚 "双喜临门" is an idiom, it probably means double-happiness arrive.It is possibly the same as the idiom "a double blessing has descended upon the house" which your people say. 2 大家在一起热闹热闹。 Let us get together, and have a fun time 3 这顿饭跟平常有什么不一样？ equals to “这顿饭跟平常（的饭）有什么不一样？” it means "What is the difference between this meal and the meals you usually have" ( I`m sorry,my English is not good , so I do not know how to translate this sentence into English exactly.) I hope it is useful to you. : )