Ok, here's the first question regarding Call of the Haunted.

Player A: Attacks Player B's Lifepoints directly with a monster

Player B: Activates Call of the Haunted and summons a monster whose attack is greater than that of Player A

Does the attack replay itself? Meaning that Player A can choose whether to attack or not. Or, does Player A's monster die because it attacked a monster who has a greater attack.

Question 2:

If my opponent activates Smashing Ground and i have only 2 monsters on the field, both with the same defense.... which one of those monsters die? Do i choose? or does my opponent choose?

Many thanks!

In your first situation, whenever the number of legal attack targets changes, a replay occurs so your opponent may choose not to attack when this happens.

For the second situaion, your opponent, who is the controller of the effect, will get to choose which monster they would like to destroy.