Runsinshadows

I’ve always gone with the convention of adding the possessive ‘s for a family name, like the Ross’s house, but not for an individual’s name, like Gus’ friend. 
(And this is why my editors want to kill me...)

So here’s the very complicated deal:
Technically, if you would actually pronounce the possessive s as a separate syllable (as you would if you were talking about the Ross family’s house), you should use an ‘s even if the name ends in s. So you would write, “I am going to the Ross’s house.”
However, in RL, very few people do it that way. They will instead write “I am going to the Ross’ house.”