Our friends have a pit bull male, with a dachshund male as well. They get along great! They're definitely partners in crime, and it's sooo cute when they cuddle together! I dont think they've ever had any problems with keeping them together.

My other friends just got a dobby puppy and they have a chihuahua mix as well. They don't go well together due to the chihuahua wanting to be dominant over this huge puppy. So far the only time they fight is due to trying to show who's dominate. Hopefully it'll end soon, cuz that chihuahua is so annoying!