1. How to activate the auto hold? ( there is no 'auto hold' button available, and i didn't find it in manual)
2. How to activate the parking brake automatically after i switch to the Parking mode? ( currently I have to push the parking button manually everytime)

1. When stopping at a light, just do a very deep press after you stop.
2. I'm certain it's in the menu, I don't recollect where though.

1. MB's HOLD is identical to Porsche's: stab the brake pedal. The system is triggered by brake fluid pressure rise time (acceleration), not by pedal travel or force. To test this for yourself, try a very slow press of the brake pedal until it can't be pressed farther. If done slowly enough, HOLD will not trigger.

Just to clarify, stop like you normally do. After you're at a standstill, keep your foot on the brake and then do a deep press of the pedal to the floor. This will engage the HOLD function. The gauge cluster will say HOLD,and now you can lift your foot off of the brake pedal. After a bit, it becomes automatic and you know how far you have to press the brake after a standstill stop in order to engage it. To get going, just hit the gas.

Since everyone else answered question one already and I have nothing to add, I will move on to question two.

For question two, you can't but if you turn off the engine it should apply the parking brake automatically especially after opening the door. (I do believe it does it anyways without needing to open the door after engine shuts off)

The above is true for the latest models. I believe in earlier models it worked a little different, but in the current models the parking brake automatically engages when the engine is shut off. It also engages if the engine is still running and the driver's door is opened. There's generally no need to manually engage it. When setting off again, it should automatically disengage as soon as the transmission is put in D or R, provided the driver is wearing their seat belt.

Interesting, I wonder when the change was made and why.

I don't know when the change was made, but most likely due to safety concerns. The electronic gear selectors got into hot water when the actor Anton Yelchin got crushed to death by his own car, because he got out to retrieve the mail or something and forgot to put it in Park. It wasn't a Mercedes if I remember correctly, but it triggered changes across the car manufacturers to ensure this would not happen again.

Interesting indeed, didn't know about that incident but my condolences.