That women is Taeha's mom not the elder brother's???? Oooh the lore deepens

That's where im a little confused, I thought Taeha was the illegitimate child

No, taeha’s mom is dead. The woman in the recent chapter is taehee (older brother)’s mom. Remember that the translation is inaccurate. The mom says “taehee” instead of mistakenly written as taeha in chapter 73 here