Question(s) on Married Filing Separately

Hi - I'm doing taxes for my daughter and son-in-law;  both are high wage earners ($250-300k each).  It appears that if each file "married filing separately" their combined tax liability for both federal & NY state is about $1K less than married filing jointly.  Does that seem logical?  I've never used married filing separately so I'm not certain its correct.

 

Also, when married filing separately, how do you handle income such as dividends or interest or prior year state refund?   Do you split them or have the lower earner claim the full amount?

 

Thanks.

Brian