No way to combine them....so if you use the "Online" software you'd need three separate accounts to model them.
Now, the desktop software has a function where you prepare a complete MFJ tax return, and then you can open a "What-if" worksheet that allows you to see what would happen if you filed each as MFS.....but if you decided that MFS was better, from what you saw in the display, you would still have to create the MFS tax returns separately. But desktop does allow you to prepare unlimited test tax files.
That said, it is pretty rare that MFS works out better than MFJ.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
