@ScarletStoner -
there are two critical requirements to claim HOH
1) is there a qualifying person? (yes, because of the new born)
2) does she pay more than 50% of the cost of maintaining the home?
if the answer to both are 'yes', she can claim HOH, otherwise she can't and would have to file single.
As far as who can she claim as a dependent, best to use this IRS tool as each situation will be unique
1) she cam certainly claim the newborn
2) if you earned more than $4300, she can't claim you, but if you earned less it is possible based on other circumstances (e.g. did you two live together ALL YEAR)
3) for your son from a prior relationship, there are unanswered questions that the tool can walk you through - it is possible she can, but it is also possible she can't,
Can SHE claim CTC for YOUR son? No, because there is no biological or legal relationship between the two of them. It is possible she could claim him as an 'other dependent" (based on a myraid of circumstances that the tool will determine for you), but she could not claim CTC for him.
IRS tool:
https://www.irs.gov/help/ita/whom-may-i-claim-as-a-dependent
