First off I'm sure you have heard this a lot but I'm sorry for your loss. As someone who is joining the military soon I'v heard that a lot of service members buy expensive new cars so this just goes out to anyone in the military or joining soon. DON'T BUY THAT EXPENSIVE MUSTANG.
What I would do is either pay off the car to eliminate a monthly expense or I'll sell it if you can still get a good amount back. Also idk if you're required to have full coverage but you could also get a cheaper insurance plan once you paid it off. Also pay off all those loans you have like family ones and the navy marine relief one. DON'T give out loans to family members. They were making it fine before the money they can make ends meet now
Put like 10K in a savings account so you can make a smooth transition into civilian life and the rest in a CD for a year. I'v heard from veterans that this helps big time. Take advantage of your TSP and put more money into it like once that car expanse is taken care of put some of that into your TPS. TSP one of the best if not the best retirement vehicles you could use.
Also use the post 9/11 GI bill. It's so much better than the Montgomery GI bill.