Hello dear,I understand your concern.
In my opinion the physical presence or absence of your sisters will not affect the periods.
But there are conditions which can affect your periods and cause delay in a regularly menstruating woman by causing hormonal
imbalance like :-
1)Physical or mental stress
If you are sexually active then the pregnancy
is ruled out by doing a urine pregnancy test.
As per your history you are not sexually active so there is no chance for pregnancy.
Usually the duration of menstrual cycle is 21-35 days.So check for the number of days and wait for spontaneous onset of periods.
Avoid stress if any and take healthy nutritional diet.
Check for your periods for 2-3 months.In case if irregularity continues then other causes like thyroid
abnormalities,ovarian abnormalities like polycystic ovarian disease(PCOD),overweight
or obesity,stress etc.
Nothing to worry as such.Relax.