Thank you all for your replies.
My mother has been diagnosed with systemic, I believe. Her stomach is at the point where she now has to have vitamin B injections and milk shake consistency food. Her hands look bad, all swollen and they thought at one point it might be lupus but I think the stomach issue nailed it down for the rheumatologist.
My step mother I think went down a similar route, I didn't have any contact with my late Dad and step mother for about 10 years, but from peoples' accounts she was tube fed and had a lung problem, so would guess it was systemic.
The only link between them is my Dad, whose mother interestingly died of rheumatoid arthritis amongst other conditions, and the years they spent living in the same location (Canvey Island). I remember when I lived there you would occasionally get some very strange smells from the oil refinery. The only other link is my Dad's occupation which was sheet metal working. I wonder if both partners were exposed to a dust of some sort from washing his overalls, or could my Dad have been a carrier of some type of virus trigger inherited from his mother?
On a side note, I might be over simplifying this, but I heard they had got a breakthrough treatment for Multiple Sclerosis. It involves destroying the faulty immune system and replacing it with a new one from the patient's stem cells. Could this be applied to scleroderma? It might not repair any damage but it should halt it.