Resolves according to a consensus of popular reporting at the end of 2028 (or earlier, if this consensus arises). If there's an open debate and reporting disagrees on the subject, or even if reporting refuses to touch this story with a 10-foot pole but most traders on here have convincing evidence supporting or rejecting this thesis, then this may resolve according to my judgment, consulting with other Manifold moderators / superusers / expert forecasters. I will obviously not bet on this market.

Yes, half-siblings count. Resolves to the spirit of the question. If her ex-husband was, say, her adopted brother, but DNA tests show no relation, his would still count as well. If it turns out they're distantly genetically related (say, third cousins), but they didn't know this, this would obviously not count. You get the idea. I reserve the right to resolve to PROB in the very unlikely event that it's actually too close to call.

For more objective and concrete related markets, see:
https://manifold.markets/bens/will-the-federal-government-bring-a?r=YmVucw

https://manifold.markets/bens/will-a-federal-court-filing-allege?r=YmVucw