how to connect 2 players so if one dies the other one does aswell

Depends on the method. If using a custom item, one player right clicks with the item on the other. The item is removed and the players display name is set as a text variable on each player. You can also use a logic variable to specify whether the player has used an item/ie connected to another player. Using target/event entity and source entity to get the names and then apply the opposite names as text variables. Then make a procedure on entity dies, check for type player, then check for logic connected = true, if so then run command with text, /kill [get text variable].

When I said "text variable" I meant [string] variable type. Go to global variables and create a new variable, set type to string. That holds text. Here's an example of procedures:

https://imgbox.com/Jk3w68MO

Second procedure would be on player [right clicks on entity] with item.

*On the second procedure, the second event/target entity should be source entity*