I don't know about India, but here in the UK, even the biggest and most beautiful house/bungalow will cost a lot less and have a very low value if it's in a small town or village (e.g. in the countryside) compared to even a small house or apartment in large cities that are densely populated. Mussoorie is quite small and less populated compared to Mumbai, isn't it? Even if Zoya sells that house, it would probably have a very low value and wouldn't even account for the huge loan that Yash had taken.
In addition, if Yash had to take such a huge loan from the bank, he probably had to mortgage some properties etc, as someone else pointed out, so that house won't be useful in any way.
Regarding Adi, when he said he hated lies (more cheaters) at the beginning, I always thought it alluded more to people who lie, cheat and hurt others in relationships, due to his past with his parents. I don't think a white lie, regarding a company, that will not really affect anyone else or hurt anyone else is part of that. If anything, it would seem to do more good for the employees than bad (but obviously not for him and Zoya, but they don't know that yet).