Background: TP and Spouse will file divorce in April 2020. They stayed in same house in 2019 and spouse travels most of the time for his work overseas. Married Filing Joint filing status used in the past. They have a primary home (Spouse's name on the title only) which the spouse paid for 100% of mortgage and property tax.  They have a prev primary home which turned rental since 2016 and TP paid 100% of mortgage, property tax and all rental expenses.

For 2019, TP came to me to discuss their situation. I did the tax return using TSJ indicators and use the Proseries Pro MFS vs MFJ worksheet and it showed MFJ saves $400.  In the comparison Worksheet, it showed TP column owed 2K and Spouse column owed $9K.  Next, Spouse when to another tax preparer and filed his MFS and he only owed $6K, he took 100% of his own income, and 100% of Itemized Deductions for Mortgage Interest and Property Tax for primary home since he paid all the payments. 

TP wants me to file her 2019 MFS. I had the chance to review the spouse's 2019 MFS Returns and noted he did not allocate this income $164K to TP and no Itemized Ded allocation to TP.  

So I don't have a choice but to include TP's income $96K without allocation to spouse on Form 8958 and she gets to have 100% of Rental activities (Rental Loss went to Passive Activities Losses). This is in Community Property (CA) State.   The couple had been keeping their finances separate although TP stays in the primary home that Spouse pays for.

Questions: 

(1) Efile: Since Spouse already efiled, will I still be able to efile TP's MFS tax return? Will I run into SSN already used in another tax return error?

(2) My understanding is for MFS, if one spouse filed Itemized Deductions, the other has to as well, even if less than Std Deductions.  In this case, Spouse took $29K Itemized Deductions and my client, TP, only had $6K Itemized Deductions. ProSeries used $12,200 Standard Deductions. I am not sure if this is correct?  Maybe I am missing some questions about MFS somewhere? Could not find anywhere in Info Worksheet. Using Itemized Itemized Deductions of $6K vs Std Deductions $12,200 is additional $1,300 of Fed Tax owed.

(3) The income allocation in this case where each spouse took their own, would they get a letter form IRS later?  Total Fed Tax owed to IRS is not a big difference.

Thanks for your time to read and give input. Appreciate clarifications.