Do either of you have Traditional IRAs already?
If you do not: you can recharacterize the 2017 Roth contributions as 2017 non-deductible Traditional IRA contributions, and then immediately convert that new Traditional IRA back to a Roth. You will only have to pay normal income tax rates on whatever gains you've earned on your $11K contributions since early January. So if your $11K of contributions have grown to $13K by the time you do the conversion, you'll have to pay income tax on $2K. (You don't have to pay income tax on the basis because they were non-deductible contributions.)
If you do already have Traditional IRAs, you should still recharacterize your 2017 Roth contributions so that you don't get penalized for making Roth contributions you weren't eligible for, but the hiccup is that your Traditional IRA basis will now be partially deductible and partially non-deductible. That ratio is what will be used to figure the tax owed on the Roth IRA conversion. For example: let's say your Traditional IRA has previously been all deductible contributions, and it started 2017 with a balance of $10K. Your Roth contributions of $11K have grown to $13K since early January, and you recharacterize those contributions as non-deductible Traditional IRA contributions. Now you have a total of $23K in your Traditional IRA, but only $11K (or about 48%) represents non-deductible basis. That means if you do a Roth conversion, 52% of however much you convert will be taxed as ordinary income. If you converted the whole thing, it would mean paying income taxes on an additional $12K, which you'd probably want to avoid at your marginal rates.
The same logic applies in 2018. If you didn't have Traditional IRAs before, you can do the backdoor Roth by making your $11K worth of non-deductible contributions, and then immediately converting them to Roth. Since you're converting immediately (rather than waiting almost 12 months after contributing), your gains should be minimal and you'll owe almost no extra income taxes.