My next trip

Next month my husband and I are going to fly to a foreign country. We got married twenty five years ago, and we want to do something special to celebrate our wedding anniversary wedding. At first we didn’t know what to do for this special celebration, then we thought that it was a good idea to go to the same place where we went for our honeymoon, Santo Domingo. In this case we will go with our sons, so we could to can show them every place what that we knew went in our marvelous trip. They are very happy and nervous because we have never done so large travel such a long trip together.
My husband and I want to book for one week the same hotel where we were before, and now I am going to book the room and reserve the boarding pass flight by internet.

Congratulations Carmen! My corrections are in red and my suggestions to sound more natural are in blue/grey.

In English, the 25th anniversary of a wedding is called the silver anniversary (or silver wedding anniversary).

A boarding pass is the ticker that you get at the airport, just before you board the plane. In your text I assumed you meant the flight reservation.

My next trip

Next month my husband and I are going to fly to foreign country. We got married twenty five years ago, and we want to do something special to celebrate our anniversary wedding. At First we didn’t know what to do for this special celebration, then we thought that it was a good idea to go to the same place where we went for our honneymoon, Santo Domingo. In this case we will go with our sons, so we can show them every place that we knew in our marvelous trip. They are very happy and nervous because we have never traveled as a group before.
My husband and I want to book the same hotel as before for one week, and now I am going to book the room and reserve the boarding pass by internet.