Q1) Can I file as married jointly?
A1) No. Her $70K income (and being a dependent) prevents you from filing jointly, even if you are getting a refund.
Q2) Who pays taxes on her income if she was a dependent that year?
A2) She does.
The family should rethink this whole plan. The best thing to do is for both couples to prepare their taxes both ways and see how the family comes out best overall, before filing,
See a similar question at:
https://ttlc.intuit.com/community/taxes/discussion/can-i-claim-my-daughter-who-got-married-on-decemb...
