Don't use silicone grease!! It's too slippery.
Brake pistons need to stick in the seals then the distorted seal will pull the piston back. Silicone grease causes them to slip too easily so the brakes don't release properly.
If brakes are binding pump the pistons right out. Carefully remove the seals, clean everything, grease with red rubber grease and replace the piston. If you don't leave it to get too bad, the seals might be reusable.
New seals at the back are under £20 so may as well replace. At front you can only get seal & piston kits for £60 a set.
Four piston calipers need a steel strip clamp and a hard wood block. Use the clamp to hold one piston in. Put the wood between the other two. Use a cycle tyre pump to blow out the remaining piston. Clean it and replace.
Move the clamp and blocks around to do the other three pistons.
Note how the seals came out so you can put them back the same way.