Had not wherewith to pay (mē echontos autou apodounai). There is no “wherewith” in the Greek. This idiom is seen in Luk 7:42; Luk 14:14; Heb 6:13. Genitive absolute though auton in the same clause as often in the N.T.
To be sold (prathēnai). First aorist passive infinitive of pipraskō. This was according to the law (Exo 22:3; Lev 25:39, Lev 25:47). Wife and children were treated as property in those primitive times.