Unearned income limit only applies for EIC, not the CTC (Child Tax Credit) or Dependent Care Credit.
Yes, non-taxable unearned income (e.g. tax-exempt interest) counts towards the limit.
No expenses, just a decrease in net unearned income. (Interest + dividends + capital gains/losses + passive activities, e.g. real estate + k-1's).
IRA/HSA/FSA/529 contributions, Sch C losses, etc, won't help. Not really much you can do about it now, unless you know of a company that can retroactively give you losses of the type listed above.
It's not as bad as it used to be, when the limit for unearned income was less than $3K, and young couples would lose $10K+ in tax credits because their grandparent did them a favor and gifted them a bond that had $3K of interest. That was PAINFUL