There's the rub. My guess is that the area is full of upper middle class and wealthy gentry who purchased lifestyle farmettes for their exurban escapes. They don't want energetic neighbors commercializing what they now consider a residential area. There can be some mighty fine lines drawn in such disputes. It's a quarrel among hobby farmers.
The District was presumably in place before the Fetterolf's bought the place, so unless there was a pre-existing business on the property, grandfathering would not seem to be in play. One would have to start by looking closely at the District rules. It's really just a glorified HOA, and that can be trouble.
We have some friends who moved out to Waterford, VA, which is a famous preservation story running back to some far-sighted people in the 1930's who anticipated urban sprawl before urban sprawl was invented. The surrounding area is very tightly controlled. It's what you pay for when you move there.
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right....
The particular Zoning Code at issue has been in place since 1968, and it clearly and unequivocally prohibits the following uses within the Historical-Rural Residential District: “Place of Worship,” “Place of Assembly,” “Commercial Venue/Event Space,” and “Special or Studio School.”
Like them or not, zoning codes that restrict or even prohibit certain uses are permissible under the 1st, 5th, and 14th Amendments to to the United States Constitution. As applied specifically to "places of worship," a municipality, under the US Constitution and federal law (i.e., the Religious Land Uses and Institutionalized Persons Act), can completely prohibit religious uses in a zoning district as long as the municipality does not completely ban places of worship from all zoning districts within the municipality, treats places of worship the same as similar, non religious uses (i.e., non-religious places of assembly), and does not discriminate between religious uses.
The Zoning Code for the Sewickley Heights Borough appears to meet these requirements in that places of worship are allowed in several other zoning districts within the municipality and the Historical-Rural Residential District in which the farm is located, prohibits just about every use that is not a single family residence or related to agriculture, including cemeteries, country clubs, cultural centers, day care centers, firehouses, recreational facilities, restaurants, and schools/educational facilities.