The stuff I have read has indicated that genetics do play a part in autoimmune disases (especially in those of the COnnective tissue group - Lupus, Sjogrens, RA etc)
I know that with Coeliac there seems to be higher incidences of family members with RA and Type 1 diabetes. The have a little connection or something.
Having said that, your genetics seem really strong in relation to lupus - that sounds like my family and coeliac. Apparently there is a 1 in 22 chance of getting coealiac if you have a first degree relative with it but my mother, my grandfather (suspected) me and two of my kids. Just seems way higher than 1 in 22.
I also have another two autoimmune diseases as well - one unidentified connective tissue diseases - possibly RA, or psoriatic arthritis (loads of symtpoms - but sero negative).
I think both our stories show excatly what I was getting at before - that there seems to be some families more prone to these things than others.