Okay, that explains it. In that case DS2's WJIV results definitely indicate deficits in phonological processing, not even in the average range (that's phonetic coding, not decoding, and refers to two of the specific phonological processing skills that are necessary precursors to attaining fluent phonetic decoding skills). There shouldn't be a problem qualifying for phonemic awareness remediation (aka Orton-Gillingham) on the basis of the 19th %ile score, as that is not just a personal weakness, but a normative weakness, in most states (except for the ones that insist on <16th %ile).
I expect the extra tests were the phonetic coding subtests from WJIV Oral Language, since that's what I would give (out of the WJIV) based on low pseudoword decoding. And maybe phoneme/grapheme knowledge (I assume that's what orthographic processing was), for the associated encoding (spelling) skills.
I think you do have the answer for twin 2. Fortunately, it's one that has a body of research with a clear remediation path.
How's twin 1's achievement testing? Low PS can be indicative of a number of things, including dyslexic/dysgraphic category profiles. Or ADHD, or perfectionism, or motor impairments (like DCD), etc. More data might help.
