I am in similar situation, except wife is in India with younger kid and I am in US with elder kid in university. I am told there is a good chance she will be denied tourist visa even if not yet applied to GC, as rest of us are US citizens. And she will be denied tourist visa after applying for GC.

That's a separate issue. If one already has a tourist visa or is from a visa waiver country, there really are no issues traveling to the U.S. while the green card process is pending if you are smart and careful. But it's very difficult to obtain a tourist visa if you are in the green card process.