You can only transfer the tax data from one 2020 tax return to the 2021 TurboTax online editions. If you need any information for 2020 on the 2021 tax return for your spouse you will have to enter that manually.
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 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.
You should usually file a Joint return which is only 1 return combined for the both of you. Make sure to stick with this one account for the future. Just ignore the other spouse's account.
Getting Married FAQ
And info on Getting Married…..
http://turbotax.intuit.com/tax-tools/tax-tips/Family/Getting-Married/INF12006.html