لَوْ أَنْتُمْ تَمْلِكُونَ
If you possessed.
In the ordinary verb «تَمْلِكُونَ», the plural wāw marks the attached subject. Once a governing verb is omitted, its attached subject marker cannot simply remain in the same phonetic attachment without the verb. The detached pronoun «أَنْتُمْ» supplies the corresponding independently expressed subject in this analysis.
تَمْلِكُونَ — you possess; its plural subject marker is attached.
لَوْ أَنْتُمْ تَمْلِكُونَ — the detached pronoun relates to the implied first predication, and the visible verb interprets it.
The omission avoids saying the same verb twice. At the same time, the conditional particle and the following verb make the syntax and intended action recoverable.