Why is it telling me "because you are married filing SEPARATELY you don't qualify for the Dependent care credit this year" when I am Married Filing Jointly?

You are confusing the income limits for the child tax credit with the childcare credit.  They are two different child-related credits.

And it sounds like you have messed up your filing status somehow when you tried to switch from a Married filing separately return to a married filing jointly return.  Try going back to My info.  Delete your spouse for now.   Whichever one of you is the primary on the return  (first name listed on the return) needs to click edit by their name.  Go back through the screens.  When it asks if you were married in 2018 say YES.  Then it will ask if you want to file together with your spouse.  Choose YES.  THEN when it asks for your spouse's information enter it and give all the information including date of birth, address, Social Security number etc. for your spouse.  Hopefully that will set up your joint return correctly.

https://ttlc.intuit.com/questions/1900923-what-is-the-child-tax-credit

https://ttlc.intuit.com/questions/1900643-what-is-the-child-and-dependent-care-credit