You are lost in labels and categories.
I suggest you don't focus on Organizations and Ethnic ties, but look at the general demographics of the era and the nation ... Knights Templar accepted into their ranks any Freemasons who held a belief in Christianity (this info can be googled and there's an article in Wikipedia)
Wikipedia contains an article on the Mechanics started out as anti-catholic but became over time ecumenical - started out as a fraternal order, subset of the adult version
The marriages of the sons were more a case of socioeconomic strata and opportunity rather than a case of ethnic identity. Given a dowry or "startup" which was often something that occurred to some extent, and still does (all those showers and wedding books etc), and proximity and a number of other environmental / worldly factors (demographics, in other words) it would be surprising to find someone traveling 1000's of miles to find a spouse to bring home when o' so many were available "at home"
Then you should separate the deaths from all else -- treat them as having nothing to do with marriage nor Organizations -- death occurs regardless of any external worldly situation or condition -- in other words, if one of the children or desc died at age two of pneumonia you cannot say it is because its father was a Mechanic and its mother was German.
And don't drag into any of this rumors or suspicion of murder, not unless someone was arrested and sent to trial and it is a matter of public record