This is a really cute idea. But it is still unsanitary whether the toilet lid is closed or
not. The reason is that they are so close to the sink where people wash their hands and brush their teeth and water from both activities splash around even onto the mirrors. You can be sure it's reaching those toothbrushes also. To eliminate the problem and still keep your cute design, put the toothbrushes in toothbrush cases that have an air hole for water to drain off the brushes and for the bristles to dry. You don't want wet bristles because bacteria can grow on them.