how rollover IRA impact my back door to Roth

Here is the time line on what happend:

1. 2012, I contributed more that we could to Roth IRA, so part of the contribution was recategorized to a Traditional IRA, say $3000 at the time. 

2. Since I didn't know there is backdoor, I let the $3000 sit in traditional IRA, which now become say, $7000

3. thi syear,  I was aware of the back door, so I contributed $6000 for 2019 and $6000 for 2020 in March this year(2020).

4. I then back doored eevrything to Roth IRA.

5. I did the samething for my husband's traditional and Roth IRA.

6. Yesterday, I learned that my husband had a rollover IRA that he did a couple of years ago (don't ask me why he didn't tell me that, we already had a long discussion on that). The amount in that rollover IRA account is about 280k.

 

I did some research online. It looks like in my case, for my husband's part, the amount I back doored to Roth IRA (12000 +7000 =19000) may most likely will need to be fully taxed due to the pro-rata rule, which means, the $12000 +3000=15000 will be double taxed.

Am I understanding that correctly? If so, is there anything I can do to fix the issue? For instance, if I ask my husband to convert his Rollover IRA to 401K, will it make any difference when I file my 2020 return?

Thank you all!