You don't understand how important jure uxoris is. Some kings by jure uxoris continued to rule property of their spouse even after jure uxoris had technically expired. I reckon Andrew's lack of blood is irrelevant if the couple is considered a single entity that becomes obsolete once one of them dies.
That sometimes works for lower titles (although it sometimes doesn't as well; it really depends on how well Andrew gets along with the liege who would make the decision, and sometimes the new title is technically a recreation of the old, rather than a continuation).
For kingdoms, it very much depends on the succession law, the relative power/influence of the two princes, and their tolerance for civil wars. In some realms, it would be perfectly acceptable for Eva to designate one of her sons as heir and disinherit the other one (although honestly, this generally went the other way, with a man with two wives favoring the kids of his second wife). In others, that would be an absolute no-no. And sometimes a compromise would be worked out.
A good example of this sort of thing (albeit for a noble, not a royal) would be the marriages of
Joan of Acre, daughter of Edward I of England. She married the Earl of Gloucester (who, critically, resigned his title and was regranted it by Edward I upon the marriage, under the conditions that said title would follow Joan). She had kids with him, he died, and then she secretly remarried. Her second husband (once the marriage was revealed) was granted the title of Earl of Gloucester for his lifetime (remember the complications of the Gloucester resignation/regrant), after which it passed on to Joan's son by her first marriage.
For a different complication, consider the succession of
Richard Beauchamp, 13th Earl of Warwick (which would play a major role in the leadup to the Wars of the Roses). He married twice; by his first marriage, he had 3 daughters, who married various nobles (notably including Edmund Beaufort, later a prominent Lancastrian), while his second marriage yielded a son and a daughter (and the daughter married Richard Neville, later famous as "Warwick the Kingmaker" in the Wars of the Roses). When he died, his son inherited as the 14th Earl, but once said son (followed shortly by his only child, briefly the 15th Countess of Warwick), Neville was able to claim the title on behalf of his wife, even though she was the youngest sister, because she was a full-sister to the 14th Earl, whereas the others were only half-sisters, even though they were all equally the children of Richard Beauchamp. Needless to say, this was a major legal dispute, and would lead to Richard Neville allying with the Yorkists against the Beaufort and his Lancastrian allies.
So, the answer to your question again is "it depends." Usually it would be the eldest son, but if the younger son had enough political support, he might make a play for things as well. As an added complication, it's quite possible that there might be a significant age difference between the sons. Again, I'm not familiar with many examples involving Queens Regnant, but kings remarrying could cause real or perceived complications for the sons of the previous marriage; Ethelred the Unready's perceived favoritism to the sons of his second wife eventually caused Edmund Ironside (son of his first wife) to launch a rebellion against his father. Conversely, when Edward the Elder died, he had children by three different wives; he seems to have divided the kingdom between his son by his first wife (Athelstan, playable in the Iron Century bookmark in CK2) and the eldest of his sons by his second wife (Elfweard, who died shortly afterwards, allowing Athelstan to reunify the kingdom), but it's not clear if that was his intention or the result of the two princes each reacting to their father's death with different sets of backers. Once Athelstan died childless, the crown passed to the sons of Edward's third wife (from whence descended future Anglo-Saxon kings of England).
