[Edit] I think I may have misunderstood originally
If I misunderstood an these actually are two Roth IRA accounts owned by you, yes, for tax purposes, all of your accounts are treated as one combined Roth IRA. When entering the amount of contributions that you made your your Roth IRA accounts, enter the combined total of contributions that you made to all of your own Roth IRAs.
[My original answer under the (probably incorrect) assumption that these were actually Roth IRA accounts opened in your grandchildren's names.]
You do not have two Roth IRAs, your grandchildren each have a Roth IRA. The amounts that you put into their Roth IRAs are gifts from you to them which are then contributed to a Roth IRA by them. For them to be able to contribute to a Roth IRA, each of them must have eligible compensation to support the contribution, generally from wages reported in box 1 of their Forms W-2 (minus any amount in box 11) or income from self-employment. Their modified AGI must also not be above the limit for being eligible to make these contributions. If these are not eligible contributions, they are excess contributions subject to penalty on your grandchildren's tax returns.
They (or someone on their behalf) would enter these contributions into TurboTax when each of their tax returns is being prepared.
