No. Dachshunds shed and, as a result, release pet dander into your home. Dander is the cause of most pet-related allergies.
All dogs are social animals and Dachshunds often worked in pairs when chasing their quarry. So, the company of another Dachshie or any breed dog is usually a quality of life improvement for these dogs. However, because they are wary of newcomers, they should be socialized with their buddies from an early age if possible.
No. They aren't mean. But they do tend to gravitate towards one favorite human, which can make others feel shortchanged of Dachsie snuggles. Many of them will also bark impolitely and at length at human and four-legged strangers.
Dachshunds are not good swimmers because of their short legs. They can learn to swim for short periods of time, but it's best to keep your Dachshund on dry land and keep a close eye on him when near bodies of water.