RMDs and the 10-year rule are two separate requirements. You have to satisfy both requirements.
An RMD is a minimum amount that you must take out of the account each year. The amount that you must withdraw each year is based on the IRS life expectancy tables, as Opus 17 outlined. The RMD is not 1/10 of the balance.
The 10-year rule requires that you take all of the money out of the account by the end of the 10th year following the original account owner's death. There is no specific amount that you have to take out each year, as long as the account is empty by the end of the 10th year. You do not have to take out 1/10 of the balance each year.
You have to take out at least the RMD amount each year. You can take out more if you want to. You might want to do that so that you are not left with a large balance that you have to take out, and pay tax on, in the 10th year. The annual RMDs alone will probably not be enough to empty the account in 10 years. Taking out 1/10 of the starting balance each year is a good way to spread out the withdrawals, and the tax, over the 10 years. But you also have to make sure that the amount you take out each year is at least the RMD amount. The RMD could be larger or smaller than 1/10 of the balance.
You can add up the RMDs for the two inherited IRAs and take the total from either account, or part of it from one account and part from the other, dividing it in any way that you like, as long as both IRAs were inherited from the same person. You cannot combine the RMDs for the IRAs inherited from your father with any other IRAs.
