Meet up somewhere where you and the dogs can be in motion all the time. Don't just pull them out of the cars on-leash in a parking lot and let them sniff. Someone (I think OC?) posted some really good information about this at one point. I'm terrible at searching.
With Meg (who has issues with dogs invading her personal space, and dogs entering our house), when I recently had a dog coming over to my house, I met up with them at a nearby reservior with a hiking trail. Took the dogs out of the car, and started up the trail on-leash with the dogs 15 feet or so apart. Pretty quickly both dogs were off-leash and running in the woods to the side of the trail while we walked next to each other. The movement and all the other stimuli kept the dogs from focusing too much on each other while they got used to being near. By the end of the trail, we were able to put both dogs in the car together, no problem.