Keep in mind that you don't have a *low* income; you're right about where the median household income is in the US. It's easy to get a skewed perspective here since the majority of regular posters make more. That said, it's definitely a good idea to look at both earning more and spending less.
Thanks,
CarSafetyGuy, for pointing this out. I think it's easy to loose perspective on what is "low-income". $49k after taxes/healthcare costs puts one just above the median in one of the richest countries on earth at one of the most affluent times in recorded history.
Dippydoo: You've taken some great first steps towards FI/RE. There's some good news coming! Like other posters said, finding higher-paying jobs will turbocharge your path to retirement, but I'm always hesitant to leave an almost perfect job (like your husband's). Also, you've trimmed most of the fat out of your budget nad it appears you've freed up a lot of cash which is currently all going towards SL reduction. For the sake of simplicity, here's a scenerio I'd use given your current jobs and income.
(using your numbers given: Current expenses (outside SLs): $23,500/yr or $1960/mo), Income (after taxes/healthcare): $49k/yr or $4000/mo)
That gives you about $2000/mo (my calculations, your numbers) per month outside of your average expenses.
Continue to attack your SLs with interest rates - knocking of SL2 first and then SL1 (put everything but the minimum towards SL2 first, then SL1). If you really can put $2000/mo towards your loans, you will have SL2 eliminated by November, and SL1 gone by March 2015. Do a happy dance, light a copy of your last SL on fire, take a picture and upload it here. Celebrate by going out to Chipotle*
The "family loan" of $27k is a bit trickier. Economically, there is no reason you should ever pay it off faster than you need to, but there are family dynamics to consider, and many would say you should pay off family loans as soon as possible as a matter of principle. I'll take the middle road and suggest that, in 2015 you increase monthly payments from $100 to $200/month. Each year you can make it a goal of increasing those payments by $25 or $50/month until it's paid off, but economically there's no reason to pay more than agreed upon.
So - that means by early next year your SLs will be gone, and you'll have ~$1800/mo to invest (after increasing family loan payments). Here's where the good news really kicks in. If you can invest all of that $1800 (instead of spending it) - then in 19 years (when you turn 50) with an average return of 7% (inflation adjusted) you will have just over $900k. Congratulations, that would give you a SWR of $36k forever. Yippie!
So: as I see it your challenges are to contine walking this narrow line you've set up for you and your husband. You can't give in to large consumeristic spending making $49k/year and still plan on retiring by 50. There's also the question of how to get your husband on board, but hopefully once he sees progress and projections of how you can become millionaires he'll come around.
On the positive side, none of this factors in promotions or windfalls. If you can funnel all extra future money you can reach your goal even faster. You also have a solid emergency fund, which should help keep your repayment and investment strategies on track.
A few finishing notes: You mentioned 401(k) balances - both of you should contribute at least as much to get the matching funds from your employers, even if this adds a couple of months to your repayment schedules. It will lower your taxes and get you an 'instant return'.
In early 2015 funnel all money from not having SL1&2 into funding your 2014 IRAs. Again these can reduce your tax burden and will be a core of your retirement portfolio.
hope that helps!
* suggestions of celebrating at Chipotle (and nothing fancier) provided by MMM himself.
note: Edited in a few spots because I'm lousy at correcting typos before hitting the "save" button. Need to work on that.