How Q is related to the one who got rank 4?

Only one person got lower rank than K’s daughter-in-law.
Q is the sister-in-law of O and vice-versa.

Q is the only daughter of K.

O doesn’t have any siblings.
That means, O must be daughter-in-law of K.

K got higher rank than both L and M but not as much as P, who didn’t get the highest rank.

Based on the above given information we have:For Ranking:

__ P > K > L, M

Again, we have:
N is the only daughter of L, who got three ranks higher than N.

Q is the paternal aunt of P, who got immediate lower rank than Q.

From the above given statement we have:

Q > P > K > L, M

Again, we have:

Q’s daughter got immediate higher rank than L’s wife.

L is not married to K.

That means, L must be married to O.

Since, M is the only remaining person, thus M must be daughter of Q.

The gender of K and M is not same.

Thus, K must be the father of Q.

Based on the above given information we have:
Q is related to the sister got rank 4