Does anyone know if it is permissible to convert existing traditional IRAs to Roths if all are preexisting?

I intend to convert both of my existing traditional accounts (one is traditional deductible and the other is a rollover traditional deductible) by depositing them in my existing Roth account. Up to this point, I thought that they must be kept separate. Now I've read that this is not the case. It will be much easier managing one account rather than doing the conversions of my traditional accounts to new Roths and ending up with three Roth accounts.

Thank you

It is permissable to put them all in one account. Some might feel it would be better initially to convert each TIRA to a separate Roth in the event you were to later decide to recharacterize one (or both) of them. After the time frame to recharacterize has passed you could combine them.

It is not necessary to keep them separate.
When the conversion is done, whether for both IRAs or one IRA, you must file IRS Form 8606 to determine the taxable potions (i.e. amounts not attributable to the non-deductible contributions) of the conversion.

Should you decide to recharacterize any portion, the recharacterization will be allocated pro-rate between amounts attributable to the non-deductible and deductible amounts.