I don't see anywhere in the ISU Constitution that specifically requires a passport to prove citizenship, whether to compete or switch.  I don't know what the permit paperwork requires.
They switched to Israel before the 2021-22 season.  I don't know if he became a citizen when his parents did, or if he claimed citizenship later.  Whether he got a passport before the 2022 changes, he knows; we don't.
Without some kind of exemption Tkachenko's citizenship and passport sounds dead-in-the-water, at least for 2026.  (Laws can change.)  They're on the young side for ice dancers, and, unless there's been some bad behavior we don't know about, 2026 wasn't a slam dunk, even if she found her Jewish grandparent in 2021, got citizenship, and a passport before the law change.  But in 2022, when the law changed, it shouldn't have been a surprise that, if she tried for a passport after the change, it was a non-starter without a change of some kind.
Even T/K aren't even front-runners for earning one of the four spots at the OEQ: they'd be one of a bunch in their point range.  They wouldn't be even if R/A hadn't biffed the RD and have come in at least 18th: in that case, then Lim/Quan, with 177 at Worlds (and 187 at Warsaw Cup) would be at the OEQ seeking a spot.