Ceiling cracks appear and worsen over weeks. Self repair or professional?
There is visual evidence in photo A3 of one or more interior renovations constructed with less than workman-like quality.

Given the age of the house and what portions of the original construction remain, I it would be common for a house of this age to have had a load bearing wall perpendicular to the ceiling joists when originally constructed.

If there was previously an interior load bearing wall perpendicular to the ceiling joists, it's purpose would have been to reduce ceiling joist deflection. The cracking in the ceiling finish is symptomatic of deflection beyond the strength of the finish joints.

I recommend consulting a structural engineer familiar with residential projects of this scope. The condition is probably repairable given a reasonable budget, but it is necessary to first know what exactly needs to be repair.