If you are legally married and have lived with your spouse at any time during the last six months of the year, you can only file as Married Filing Jointly or Married Filing Separately. Filing as MFS in most cases is the worst way to file from a tax standpoint.
See this TurboTax support FAQ for filing jointly versus separately - https://ttlc.intuit.com/community/married/help/is-it-better-for-a-married-couple-to-file-jointly-or-...
If you still decide to file as Married Filing Separately, then for all joint accounts you can split the income received any way that you want as long as it is not over 100% of the total income received. Unless you live in a community property state, then other rules apply as stated in the support FAQ provided.
