If you buy a house, the government will issue you a residence visa for 99 years, I guess, as long as you fulfill other visa requirements.
This is technically incorrect. I believe you are confusing the 99 year lease period on certain property in the UAE with residency visas......a totally different thing.
When you are employed by Emirates they sponsor you as their employee. Emirates (as your sponsor) provides you with both a residency visa and a work permit (they take care of the application process and pay the fees).
Once you have your residency visa you can sponsor your wife/kids. Should your wife decide to work she would have to apply for a work permit for herself (this is normally done by the employer who she would be working with so it isn't normally a big deal).
When you buy property it will come with a "promise" of a residency visa. This visa will be similar to the current residency visa (required to be renewed every 3 years at your own expense) but will not allow you to work within the UAE (will not come with a work permit). This visa associated with the purchase of real estate purchase is the same whether you have purchased a "freehold" or "99 year lease" property.
Hope this helps?