Don could show anger, and then he could let his anger simmer, showing no visible signs of it, even as he seethed below the surface.
He was not expecting such a retort, and not delivered in such a... threatening tone. "Don't be ridiculous, Guilian. How dare you take that tone with me. This foolishness will end now, and you will return home, and nobody will be in danger."
He pondered his next statement carefully. "Damian and Verity are there. We're hoping they'll stay until the twins are born. You want to be there for your nieces, don't you?" He knew of his younger son's... obsession for Verity. She was so loving, it was hard for any man not to be enamoured by her. Guilian had always followed her like a giddy schoolboy. If that didn't get him home, then he doubted anything would.
Of course, he realised that the Lestranges could continue Guilian's patronage at the Casino, and he conceded. "Very well, but if you insist on staying, you will find no more funds coming to you from your trust." WIthout money, he'd not last very long in this place. "If you come home, I'll see to it you have all the funds you need."
When in doubt, always threaten to revoke the trust. It had been threatened to Damian, and now, much to his own reluctance, he'd needed to use it on Guilian. He prayed to Merlin, and to God that this nonsense would be over soon. Did Guilian not realise how much everyone worried about him?