Good afternoon
I have just got my mtb out after long time and having brake issue the front brake is nowhere near as strong as rear is this normal using disc brakes

No, generally most feel that the front brake is the more powerful one (and at the limit of going over the bars it becomes the only brake. Does the lever pull feel solid and remain the same after repeated pulls? The two first possibilities are the pads are contaminated with something that reduces their friction (or are badly glazed) or if the brakes are hydraulic there's air in the line. Andy

I have removed the pads and sanded and cleaned disc but still same
When I pull leave it doesn't go solid but the piston move ??

What kind of disc brakes are these? Brand? Model? I think it is now time to check the brakes themselves and it sounds to me like you may want to take it to the shop to have it done right by people who have done it hundreds of times.

Maybe air bubble in the hydraulics (assuming it's hydraulic brakes).

It sounds as if the brake needs to be bled, to start, but specific tools are needed and since it is a safety item someone who is skilled should probably do the work as Leisesturm suggests..