16-50 is a good choice. You'll appreciate the extra 2mm width (compared to zooms that start at 18mm) when photographing buildings.
Leave the 70-200 at home. That focal length can cover architectural details or some of the weird characters walking around, but you already said this is a family trip rather than photo trip. Family gets bored when you loiter for 30 minutes taking close ups of gargoyles and window trim
Your primes might not see much use. 35mm/2.4 doesn't offer much that you don't already get from the 16-50/2.8. One of your 50mm primes provides better low light and thin depth of field, so maybe bring one of those. For night cityscapes 16mm/2.8 is IMO more useful than 50/1.4 but having options isn't bad. Maybe go out with a 50 after the family is in for the night. Which 50? Do you value autofocus or maximum aperture more?
P.S. You mentioned buying a wider lens. I'm selling a Roikinon 14 and a Tamron 10-24. I could meet you near B&H or downtown if either fit your budget.
Pentax DA* 16-50; Tamron 10-24; Rokinon 14mm - PentaxForums.com