Due to labile bp, cardiologist said for 90yo to take 5 mg lisinopril in am and at 4. Sis gave 10 in am, said 'its mothers day' what's wrong with this?

Nothing probably. Lisinopril is usually given just once a day. So there is not really an advantage to taking it twice a day as it is long acting. The starting dose depends on a number of factors such as how high the blood pressure is and the kidney function. Not sure what the significance is of the comment about mothers day.
I have nit a clue as. To what your question is. Please rephrase. Thank you.