"They" can work. Here is Ann Nyland's translation of 1 Tim 3:2: "So then it is necessary that they are blameless, and faithful to their partner…"

But to me, the 'partner' in view here is the theological figure of the Bride of Christ—often spoken of by Paul as if a real human woman (2 Cor 11:2, etc.).

A leader who is faithful is being faithful to her!