I'm a little confused about the circumstances of the barking. You ask if you should keep he dogs inside the house, but also say that they don't bark when they go outside. So I'll try and be comprehensive with my answer.
First, I assume your dogs are meeting the guest dog at the meet and greet, where you can go much more slowly and have more control over the introductions to help keep your dogs relaxed around the new dogs and people. If not, this is your first step. If everyone has already been introduced, I don't see any reason why your dogs need to be part of the drop off process. I often kennel one or both of my dogs (only one is really excitable) for the drop off just to keep them out of the way as stuff is being brought in, and to give the new dog a little time to relax before having to interact with my dogs. They've already met, so I know they'll get along, but that transition time is just a little stressful for everyone, so I just avoid interactions during those exciting times when all of the dogs are more likely to reach their excitement-stress threshold. Your dogs may still bark, but at least they'll be away from the bulk of the action, which will likely make them more comfortable.
As for getting the dogs more comfortable with strangers, work on some desensitization and counter conditioning exercises with them. There are a lot of great games you can play with them to get them to relax and start to think of strangers as fun, but this is my favorite because it's simple to do, and very easily modified to fit your specific case: https://paws4udogs.wordpress.com/2012...
If the reactivity with strangers is only happening at your home, you may need to enlist a few friends who don't know your dogs well to help by spending an afternoon coming and going from your house while you manage your dogs. You'll likely have to focus on teaching them one dog at a time, since dogs learn best when they have your full attention. You can also keep a container of treats at the door and train your guests to ignore the dogs but periodically toss treats in their direction while they're there, but this requires the willing participation of quite a few guests. Initially, the dogs will just associate the treats with the person who is providing them. It takes quite a number of repetitions of the game with different people for them to start to associate ALL visitors with good things, not just a select few. With the Watch the World game, since you're the only one providing reinforcement, you don't have to rely as much on the participation of others and your dogs will more quickly generalize the game.
Thank you, I also will try this with my chihuahuas. ♥♥