RFLP Pedigree Analysis Question

[MikeJ]

Hey all!
I've been struggling with this question for almost a week now, and I seem to misunderstand some principles leading to a solution. I hope anyone could help out!

Here it goes:
Consider the following pedigree, showing a disease in humans. The DNA sequence causing the disease is known. 
A group of researchers has prepared a probe for the entire mutant DNA sequence, used to yield the following southern blot.
Assume that the probe can identify all possible alleles for the mutant gene (A/B/C). Note that the thickness of the band is meaningless. 

A) Predict the hereditary mechanism for the following disease.
B) Both parents have had two more children; a boy and a girl. Southern Blot procedure for both has shown that the male showed a band for B, and the female showed a band for B as well as for C.
Determine the phenotype of the two children.
C) Can you find any evidence for crossovers in this pedigree? If so, where? 

A) The hereditary mechanism is probably X-linked recessive.
Now, what I don't get here:
Male I-2 has allele A, coding for the disease.
Male II-1 has allele B, not coding for the disease, while Male II-3 has also allele B, coding for the disease. 
If so - what is the allele coding for the disease? Is it A? Is it B?
If this was the crossover, why aren't we observing a band also for the recombinant allele? 

It looks as if something is missing here, or I'm just not getting it. 
Does this make any sense to anyone here? It'd be highly appreciated!
Thanks!