Should I do kegels sitting up or laying down

My muscles are very weak.I do 2 second holds,rest for 10 seconds then hold again.

Traditionally a sitting position - and from a classical yogic point of view that would be any cross-legged asana - will allow you to observe and experience the contraction and release well. But kegels can be done while walking, standing, sitting, laying, and in the beginning establishing a regular practice that gives you better strength and control, in any position, is what matters most.

You can do them anyway you want, even hanging upside down. But for me the best position is sitting, back straight.

Best would be in every position. erect kegels. flaccid kegels. short kegels. long kegels.
stretched kegels. clamped kegels.

Its a muscle and muscle that is used in different variations is a more functional muscle then when you do just one movement.