I've always been able to remove those turbo-to-manifold nuts without too much trouble but our cars here in the western US don't rust. Where you are, corrosion may be part of the issue.
Heat always helps.
The turbo-to-downpipe nuts often take the studs out with them but that's not really a problem.
As a last resort, removing the whole manifold is no big deal, and those nuts almost always come off with minimal trouble.