You've got nested functions and you're accessing large amounts of data? That's a major design flaw. The only way to improve performance is back out of the use of multi-statement table valued functions and start addressing the T-SQL directly. The inline functions might be a good idea, but don't nest them. Otherwise, regular T-SQL queries are usually the best approach. If you really need to break down the code, which is a valid approach at times, then use temporary tables because they will provide statistics making queries that JOIN them or search against them more efficient.

Also, one suggestion involved the NO_LOCK hint. I'm very wary of hints in general, but the NO_LOCK hint in particular is especially dangerous. Understand it thoroughly before you apply it.