Deedal, hello & a great big welcome! Have you seen the "sticky posts" (permanent info posts) at the top of the thread list? There are several on SLE & one on APS.
I really recommend a trip to your library or bookstore. In his lupus hardcover, Dr. Daniel J. Wallace devotes pages to APS; he covers how many people with lupus have APS & vice-versa; how many APS patients are symptomatic enough to actually require treatment; what the treatments are for people who've not had an APS "event"; when he reco's baby aspirin vs. Plaquenil; etc. He discusses MS briefly in several places.
Dr. Wallace lists conditions other than lupus in which ANA can be positive. Also, he lists specific autoantibodies seen in lupus: there are as many as sixteen (wow!) on his "short list". QUESTION: Can you see on your labs whether you've had specific tests that GO BEYOND the ANA test? e.g., anti-ds-DNA, anti-Sm, anti-Ro, anti-La, anti-neutrophil, anti-histone, ETC.?
FYI, another top rheumie/author is Dr. Robert Lahita.
Whether your DIL's suspicion---that your rheumie prescribed Plaquenil to reduce the effects of antiphospholipids---only he can say. With what you cited---weakness, loss of feeling in foot, etc.---coupled with your family history (MS), your disc problems, etc., there's a lot to sort out!
On tingling & numbness: My mind just wandered in some other directions (it does that
)... Is your blood sugar considered elevated (is diabetes a possibility)? Have your thyroid levels been checked as a matter of course? Any possibility of anemia? (I only mention those things because of problems I've seen in my family/friends, and me, too. I suspect my tingling was likely due to anemia. It stopped a few months into Plaquenil.)
I hope you stop in here again soon & am looking forward to your ongoing updates. Meanwhile, all best wishes! Sincerely, Vee