Thanks for that response. Maybe the mourning period varied slightly over the years. In the site I had looked at when I started this story, it said 2 months for an uncle or aunt, and then two years for a wife who lost a husband, but only 1 year for a husband losing a wife.
Maybe the difference between the 3 months and 6 weeks for an aunt or uncle might be if they were an aunt/uncle by marriage?
So by that reckoning, they only need to mourn officially for 6 weeks, but because they were close with Mrs Gardiner, 2 months was considered an appropriate mourning period.