I think yorkies pose a lesser risk than other dogs, but it really depends what kind of allergies the person has.
Some people will just sneeze or itch, and others (like myself) develop asthma and have a hard time breathing around allergens.
I'm personally allergic to dander and saliva so I chose the lower dander breeds, but still have to take 3 daily medications, so it really is a gamble.
Also -- allergens can change and grow over time, so what you may not be allergic to now, you can be in the future (I'm dealing with this right now).
But if it's just for short visits I would *guess* your family would be fine coming over, since they don't have long term exposure
