Find and Mark Twins (How To)
Identifying multiple births can be very helpful. Family Historian can help you find and mark them.
The following expression can be used in a query to spot multiple births (note it will only find matching dates so if you have 2 children with just a year) it will mark them as twins.
=IsTrue( (%INDI.BIRT.DATE% = Field(NextSib(%INDI%),'INDI.BIRT.DATE') ) or (%INDI.BIRT.DATE% = Field(PrevSib(%INDI%),'INDI.BIRT.DATE') ) )
You can then use the results to set a Flag for future use, or if you prefer, simply use the expression directly in a diagram to condition an icon or other box attribute.