Q:

what is the meaning of "had they used their gift"? does it conditional?does "as D.D. Home used his" means that he should followed the advise?

what is the meaning of "had they used their gift"? does it conditional?
does "as D.D. Home used his" means that he should followed the advise of the author?

To realize their position one has to remember that they were little
  more than children, poorly educated, and quite ignorant of the
  philosophy of the subject. When a man like Dr. Kane assured Margaret
  that it was very wrong, he was only saying what was dinned into her
  ears from every quarter, including half the pulpits of New York.
  Probably she had an uneasy feeling that it was wrong, without in the
  least knowing why, and this may account for the fact that she does not
  seem to remonstrate with him for his suspicions. Indeed, we may admit
  that au fond Kane was right, and that the proceedings were in some
  ways unjustifiable. At that time they were very unvenal themselves,
  and had they used their gift, as D.D. Home used his, with no relation
  to worldly things, and for the purpose only of proving immortality and
  consoling the afflicted, then, indeed, they would have been above
  criticism. He was wrong in doubting their gift, but right in looking
  askance at some examples of their use of it.

from http://gutenberg.net.au/ebooks03/0301051h.html

A:

Margaret and the others are using their "gift" for some sort of material gain. D.D.Holme used his gift not for worldly gain, but for other purposes. The passage says that if the girls had used their gift the same way that Holme used his gift, they would have been above criticism.

