On a joint tax return (for a married couple filing jointly), it does not matter tax- wise which spouse appears as the Primary taxpayer. The order does not affect your tax credits or tax calculations. But it is advisable to keep the order consistent year-to-year to avoid processing delays.
Both spouses are equally responsible for the accuracy of the return and the taxes due.
Some info if you both used Turbo Tax last year.
You can not transfer from or combine 2 returns or accounts. Just pick the return for the spouse that has the most complicated return to enter or has any depreciation or business or more investments. Or use the account/return for whoever you want to be listed first going forward (by the way you can not change the order of the names). Then add the other spouse's name, ssn and info to it.
But if you want to keep the prior accounts separate from the new Joint account then start a new account. Online is only good for one return per account. But you can use the same email address for 5 accounts.