Rulings on Performing Masah Over Hijab and Praying While Seated

Yes, performing Masah in that way is correct; simply passing your wet hands over a few hairs (at least one-fourth of the head) is sufficient. To ensure your Wudu is valid without removing your hijab:

Wetting your fingers and sliding them under the front or side of the hijab to touch the hair is the proper way.

Regarding the confusion about 'gestures' (Ishare): When you pray while sitting, you naturally have to bow for Ruku and lean further down for Sujud. This very act of leaning is what is meant by 'gesturing.' If you were to sit perfectly still without moving your back or head, how would you distinguish between Ruku and Sujud?

When you are in an emergency or have a genuine medical limitation (like your leg pain), you do what is within your capacity. You stand for Qiyam if possible, fold your hands, lean forward for Ruku, and lean down further for Sujud. There isn't one 'fixed' rigid posture for this; the key is that your Sujud must be lower than your Ruku. You are not required to go down to the ground floor to pray, especially since there is no congregational prayer (Jammat) required for you there. May Allah grant you ease. Ameen.