you could file joint and include form 8379 innocent spouse allocation. it would seem that since you were married when he died the only options are Joint or Separate returns.
you can claim the exemptions for the children in III of form
without knowing a lot more I can't say that this would maximize your refund. you may want to use a TT pro TT live or a professional cpa or law firm
as you know most credits and some deductions are lost if filing separate.
