In almost all situations, it is more beneficial to file Married Filing Jointly than Married Filing Separately.
Please read this TurboTax Help topic for more information.
If you wish to file separately, you have to use two different online accounts, one for each spouse. You cannot use the same account for both spouses.
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regarding accounts, you can do it that way but it is expensive.
It is cheaper to use the CD/download version of TurboTax on your computer.
visit the IRS at https://www.irs.gov/filing/free-file-do-your-federal-taxes-for-free
to find truly free filing. Note that some include free state as well.