Salaam Alaikum,
Is it Permissable to not wear the hijab in front of.... my grandma's brother (My dad's mom) from my dad's side and my mom's sisters' husband who is probably in the 60's+ range in age?? Do I have to wear hijab in front of them?
Jazak'Allah khair.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

The brother of the grandmother from the father’s side is the maternal uncle of your father, so he is like your maternal uncle. Hence, he is one of your Mahrams and you are not obligated to wear Hijab in front of him. For more benefit, please refer to Fatwa 91660.

As regards the husband of your maternal uncle, then he is not your Mahram just because he is the husband of your maternal aunt, but if you and him suckled from the same suckling mother, then he is your Mahram and you are not obligated to wear Hijab in front of him. Otherwise, he is not your Mahram and you are obligated to wear Hijab in front of him even if he is over 60 years old for the general texts that order women to wear Hijab and indicate that it is obligatory for them to do so.

Allaah Knows best.