I invited people to come to my house for a long weekend for Christmas markets. We all had a wonderful time together, and agreed they would visit this year. Should I remind to come?

Yes. They probably haven't forgotten if they all had such a great time, but if you remind them, you're letting them know that you are happy to see them again this year. You can be very casual with your reminder; use social media, telephone or write. Just tell them that you are really looking forward to the Christmas markets and catching up with them again. You don't have to use the words remind or invite, just make contact so your guests feel welcome to enjoy your hospitality. Anyone that can't make it this year will have a chance to tell you too so that you won't be left wondering who is and isn't going to come.