I looked for the Tokina you are referring to. I'm assuming it's the ATX 287 Pro SV? 28-70 mm f2.8, angle of view is approx 75-34 degrees through the range.
Then I took look around my local shop's website for references:
Henry's Camera Canada Photo - Video - Digital Camera's
The two Sigmas you mention are not in stock at my local shop. Special order item, but this particular Sigma 18-50 mm f2.8 DC EX popped up in stock so I checked its specifications in further detail.
It does not have as much length but I don't understand why it is tighter (about 69-38 degrees - helpful for you). It's in stock at my local shop at about $430 USD but I know they should be cheaper around you (especially when the 24-70 is selling at $512 USD at my shop - ouch).
I don't know much about this lens, but the 18 mm should be more helpful in those tight room situations you speak of and you don't want to use flash. With my kit lens, I often find myself shooting around 18-24 mm in a tight room situation.
So I find this 18-50 mm would be a little more versatile for your needs. I'd give it a try or see if Joe is willing to switch to this lens in exchange for the Tokina, since he prefers the wide shot anyway.
A couple online reviews I found:
Sigma 18-50 mm f/2.8 DC EX Lens Review Sigma 18-50/2.8 Lens Review
As for the prime in the 40-50 mm range. It's going to be tough finding the autofocus 50 mm f1.4 Pentax lenses in stock. I'd keep hammering the websites and snap at the first opportunity. Alternatives - have you tried checking the Pentax 43mm f1.9 limited or DA 40?
Hope this all helps!