I think that they didn't considered the implications of the rules back in
2010 or in
2011. They were correct in insisting that you and your sister apply independently from your father, as he could not include dependants in his Long residence application. However, they could have delayed your father's ILR and granted you and your sister ILR at the same time as your father under 198.
Unfortunately, this possibility was not in their guidance of
2010 and
2011 and probably nobody thought of it in this way.
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