There was a very obvious plan here that Barty almost mentally kicked himself for not thinking of immediately. There was no way these people knew who he and Chas were. If his sources were correct, they didn't even know who their daughter was which wasn't any skin off his back. After all, he only needed the golden trio to know who these two were.
"Fancy dessert, darling?" Barty inquired in a teasing tone with a small, mischievous grin spreading across his face. They could get close, alright. The table next to the pair, for example.