Minecraft – What command can I use to detect when any player is in a certain area

Any selector arguments you use in testfor can be used in tp. Like so:

1.7 to 1.12: /tp @a[score_HEALTH=1] X Y Z
1.13+:       /tp @a[scores={HEALTH=..1}] X Y Z

There are problems with using low health to check for death. Instead, I'd recommend adding a deaths scoreboard:

/scoreboard objectives add deaths deathCount

This score will get set to 1 when a player dies (automatic, because of the type of objective), your commands can teleport players with a deaths score of 1 and then set it back to 0 (so the player isn't repeatedly teleported).

The following commands are a full solution, including the team score incrementing, for 1.13+:

tp @a[scores={deaths=1..}] 73 10 31
execute as @a[scores={deaths=1..},team=red] run scoreboard players add blue points 1
execute as @a[scores={deaths=1..},team=blue] run scoreboard players add red points 1
scoreboard players set @a deaths 0

You can make a redstone clock (I recommend the repeater ones) and attach it to a command block with this command:

/spawnpoint @a X Y Z

Remember to turn off command block output to prevent spam!

/gamerule doCommandBlockOutput false

Hope it helped. :)