Unfortunately you can't carry them both forward into a single return (this is the same whether you are using the online or desktop products). What you'll need to do is carry forward one (probably best to do the one with the more complex carryforward info if applicable). Around the time it asks you your marital status you can choose the option to prepare the returns together. As you go through the interview you will have to manually enter any carryforward for your spouse.
If you do this, next year you will be able to carryforward the data for both returns together.
