Kinda overwhelmed could really use some advice.

I'm going to try to make this straight to the point. I spent about 2 in a half years in the army enlisted at 17 got out 20 with a med board rated 40%. It took me about 6 years to actually get with the VA and finalize everything and receive benefits. That was completely on me I was terribly depressed and had a rough start getting on my feet. I can't explain why but I couldn't bring myself to receive the benefits. Instead I started an apprenticeship as an electrician and worked my way up the ladder. I'm now 27 and between VA benefits and my jobs pay I make about 58k to 60ish k a year which is actually livable where I'm located (south Carolina). Here's the problem for those 6 years I spent putting myself together I never worked on my credit. Everything I bought including cars rental homes I've stayed at have always been put in someone else's name to save money. Didn't get my license until I was 19 so car insurance was always outrageously high and everywhere I've lived had roommates who handled bills and such. There's never been an issue with me paying my share everyone who knows me has complete trust in me. But until 6 months ago I had no credit history. This has caused me some issues the first line of credit I ever opened was for my personal car. I got it from a buy here pay here dealership and after signing everything I ended up owning around 18k for a 7k car. Payment on it is 401 a month because my best friends mom co signed for it with me. Insurance is 200 as she added me to her plan. Next I opened a secured credit card with Navy fed and was going to use those lines to build credit. Well about 3 months ago my older sister and her husband split up. They have 7 kids together and have always struggled. They were together for around 10 years her husband always worked and did the best he could to provide but it was like every 7 or 8 months my sister was pregnant. Before anyone says the obvious like they should've been more careful or responsible take my word for it when I say they've both come from some of the worst backgrounds you could imagine. I won't go into detail but you could make a horror story from half the things we all went through as we were growing up. I'm the youngest of all my siblings but honestly just had better friends who took care of me a long the way and made sure I got to where I am today. That being said my sister called me broke down in tears asking for help because she had nothing to her name no skills besides raising children and absolutely no help besides going to me. She needed a car to get a job and asked me to help her. I spent almost everything I had left in my bank after a nasty breakup to put a down payment on something and get her on the road. Well the only place that would finance a car with my credit being so new was drive time. As everyone knows that was an awful idea but I had to do something fast. At the moment I owe around 16k on my car and almost 20k on hers. Due to my low credit history I was only offered insanely high interest rates. As of now I've never missed a single payment and managed to bring my score up to 680 to 700 depending on where I check it. I tried getting one of the vehicles refinanced through Navy fed but was denied due to short credit history. I genuinely don't know what to do and have been looking at 3rd party lenders to maybe take out a loan and hopefully pay less then 30 something % interest on the vehicles in my name. Currently not having much luck but also haven't branched out much. Can anyone please guide me just a little. I have no one older to help or talk to.