Second problem: the sin committed (idolatry) is a mortal sin in Catholic theology — which disqualifies them from purgatory

In Catholic doctrine, dying in a state of mortal sin means damnation, not purgatory. Purgatory is for those who die in a state of grace with venial sins or unserved temporal punishment. But the soldiers in 2 Maccabees committed idolatry — a mortal sin. So if this passage supports purgatory, it contradicts Catholic teaching on mortal sin: it would mean you can be prayed out of purgatory even after committing a mortal sin.