I have two huge musts ... 1 when you let them out of the crate they must go straight outside and make sure you go with them even if you have a fenced yard because number 2 is the most important part ... 2 praise praise praise! Tell them they are the most wonderful dog ever when they do their business outside. They do love treats and that is fine but I believe the most important thing is to let them know how happy they make you when they "go" where they are supposed to. I never use punishment when they make mistakes because they are such emotional little critters. A Dachshund that loves you will want nothing more than to make you happy so show them what makes you happy.
Yes this can be a long frustrating process but it will get better. Unfortunately some never like the rain or cold or snow but some eventually will even brave these horrors just to earn your praise and pets.
It took a long time and a lot of doxies to teach me this lesson, we owners can be hard headed sometimes but they are finally getting me trained.
Dachshunds are really clever, they need to be kept busy or can be naughty if bored etc. They also need exercise, even though they are small dogs they need plenty of stimulation and exercise to keep them fit and healthy. Most are very food orientated so this helps with training. Consistency is the key, but you do need to be a "pack leader" or they can soon try to take over!!
They are such lovely dogs to own, so much fun and real characters. With the right amount of time and love invested at the start they pay you back a million fold times over. There is plenty of help available here on the site so don't be afraid to ask for help.
Good luck and enjoy your babies and don't forget to post us some pictures!