Question 3 under “your spouses personal info” is coming up as an error because I’m preparing the return for my husband and me; not a child.

My husband and I got married in 2018 so this is our first return together. How do we “link” to each other? 

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Sounds like you are doing it all wrong.  Here's some general info on getting married.  Did you both use 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 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.

And info on Getting Married…..
http://turbotax.intuit.com/tax-tools/tax-tips/Family/Getting-Married/INF12006.html
 
Is it better to file Joint or Separately?
https://ttlc.intuit.com/questions/1894449-is-it-better-for-a-married-couple-to-file-jointly-or-separ...

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Question 3?  The one that asks if anyone can claim you?  Say No for each of you.  Or is your parents or his parents claiming you/him?