Staffie,
I agree that 8 weeks old is far too young to base a future relationship on :) It's also possible that as soon as she reaches maturity, the 'female mystique' will take over and they'll all be best of friends..
Still, just a caution... if this does happen in the future and they do become friendly. I'd recommend that when all three are together, don't ever leave them alone for any length of extended time without crating 1 or two of them.
You have two terriers and a hound in that grouping. The two-- male/female-- are already buds and there's an uneven distribution of size, age, and personality types. It only takes one spat for something really bad to happen :(
If they lived together for any length of time, I don't think it would be as much of a concern...but the whole 'visit' thing where food/beds/toys and new/revisited territory are involved, creates too many possibilities for fight incidents to happen.
Sorry, but that's jmo. :(
But wait and see what happens with maturity before you decide anything permanent with this 'relationship'.. Your dax could just feel threatened by the whole 'wittle puppy' thing... I wonder if there's any change when it's just the dachs and the Yorkie... perhaps they can work things out if the Staff is pulled away from the mix (in another room or outside? )
best of luck,
toodles