Hello!
If your dogs have been socialized with other dogs and are generally friendly with each other and other people and animals then I don't forsee any real problems with introducing a new dog into your 'pack'. Just remeber to take it slow and it might take a little bit for everyone to get used to the new member
Just remember not to play favorites with the new guy just because he is new and still give your other dogs equal attention and love; you don't want to create sibling rivalry
Maybe to get them used to each other and have the new guy be accepted faster you can do some fun activities together like taking them all for a walk or playing together outside; just some fun possitive activites where they are all interacting together. Other than that I don't think you will have any major problems.