Crate and rotate. No high value items out when they are together, and never leave them unattended together. If it seems that the pups don't get along at all, then never put them together. As they get bigger, there will be a greater chance of the Dachshund not surviving altercations.
Dog aggression is a very real thing in bull breeds. It doesn't go away. It is genetic and can't be "cured" or "trained" out.
Multiple dog homes with bull breeds can be very difficult to work around. Especially when it becomes a crate and rotate situation. If you aren't prepared to crate and rotate, then you should look into re-homing the Dachshund and possibly one of the bull breeds. Or both bull breeds and keep the Dachshund.
"i can explain it to you, but i can't understand it for you."