As to "shared facts". This is a term invented by FTM as a politically correct version of family and/or marriage facts.

In reality these facts (in GEDCOM Family_Events) are limited to:

Marriage, Divorce, Residence, Engagement and the like.

FTM does need a true "shared fact" data entry scheme, for times when a group of individual share an event, such as a residing at a particular place on a given day. But IMHO this type of entry has its limitations. Since many times an event can happen over a period of time, therefore some events may have individuals involved in that event participate for various periods of time, this means the data entry screen must allow for person specific dates. Some individual facts lend themselves better than others to be shared. Emigration, Immigration, Naturalization, Census, are some that are better suited.