All of your Roth IRAs are qualified because you are over age 59½ and it has been more than 5 years since the beginning of the year for which you first made a Roth IRA contribution. Because your Roth IRAs are qualified, any distribution that you take from any of your Roth IRAs is free of any tax.
As you said, your Roth IRAs are treated in aggregate as if all of the funds were in a single Roth IRA. Technically, your contribution basis still comes out first no matter which Roth IRA the distribution comes from, but that is pretty much irrelevant since your Roth IRAs are qualified. You basis in Roth IRA contributions and conversions belongs to you, not to any particular one of your Roth IRAs.
