Can you use both the montgomery gi bill and the chapter 35 simultaneously for college?

Check with VA. Although your father was a disabled veteran, GI Bill normally requires formal transfer to dependents. Drilling reservists may get Montgomery GI Bill, but there are special requirements and significant paperwork
https://www.va.gov/education/about-gi-bill-benefits/montgomery-selected-reserve/

They both have limits on how long you are eligible. I believe the disability benefits should be used first.

Dude...

I’m no VA Benefits Specialist nor pretent to be on, but I’m pretty sure you are on your own!

If your Masters is in IT, just looking at your MOS. Do you know about VET TEC?

https://www.va.gov/education/about-gi-bill-benefits/how-to-use-benefits/vettec-high-tech-program/

And if your Masters is in STEM related field you can get an extension on your post 9/11

https://www.va.gov/education/other-va-education-benefits/stem-scholarship/

https://www.militarytimes.com/education-transition/2020/01/13/court-rules-again-to-give-veterans-access-to-both-post-911-and-montgomery-gi-bill-education-benefits/

From Jan:

"Last week, the U.S. Court of Appeals for Veterans Claims issued its final ruling on the case of “BO vs Wilkie,” letting stand an earlier decision that the Department of Veterans Affairs practice of making veterans relinquish their Montgomery GI Bill eligibility in order to receive Post-9/11 GI Bill payouts is improper.

Federal officials argued in court that the arrangement is designed to make sure veterans aren’t doubling up on their government benefits for personal profit. But the court rejected that argument, saying that instead veterans eligible for both programs should receive each set of payouts, just not simultaneously."

"That means that veterans who use up their 36 months of Post-9/11 GI Bill education benefits would still have access to 12 months of Montgomery GI Bill benefits if they paid into the program while they were serving. Under existing federal statute, any government higher education payouts are capped at 48 months."

https://www.militaryonesource.mil/military-life-cycle/veterans-military-funeral-honors/which-gi-bill-is-best-for-you

https://www.va.gov/education/survivor-dependent-benefits/

Honestly with Post 9/11 alone should cover a Masters degree. I have two Masters. The first one I used primarily TA and then 9/11 GI when I couldn't pay what was left after TA. And then I had 30 months left so I got a second Masters.

You are probably referring to VA DEA. That requires you to be under 26 years old when starting to draw that money. Chapter 35 ??? of what ?

There are some educational benefits for Reservists. The link is more "big picture" overview, than anything else, but it should give you an idea what might be available from the Reserves.

You may also want to check with your state to see if they offer education benefits. I inquired in my state when I was working towards my Masters, but as I was already getting the Post 9/11 GIB, I wasn't be eligible for anything from the state until I exhausted that federal benefit, which was fine.

https://www.goarmy.com/reserve/benefits/education.html