Citing a paper under review in 2 different conferences
Normally, you can update citations until the proofreading stage.  I've done that at more than one occasion.  When submitting the article, I cite Myself et al. (submitted 20xx).  Then the manuscript goes through peer review, revisions, subsequently typesetting, etc.  By the time the final proofs come out, I probably know whether Myself et al. is rejected or not, and can probably provide an updated citation.  In the worst case, I can replace it by a short text that this will be considered in a future publication.