1) I just wanted to ask if after 2nd rakat you recite the word "behawlillah" or a couple of words but not the whole phrase and realize you didn't recite tashahud, do you immediately sit down and recite or get up while reciting the whole phrase and then sit back to recite tashahud?..

2) In a 4 rakat namaz, you doubt after 1st or 2bd sajdah if it is your 3rd or 4th rakat, what do you do?

1- When you realize straightaway you sit down and read tashahud without finishing behawlillah
2- In this scenario read tashahud and finish namaz. And read one rakat ehtiyat afterward