So, some advice.
First of all, ensure everyone understands how Second Wind works, and that a Heal check from an adjacent buddy can help someone who's in negative HP.
Second, tactics are fairly significant here. If your Fighter isn't using his mark, and locking very potent enemies down with his Combat Superiority/Challenge feature, then he's doing a bad job. If your Paladin isn't marking potent foes, and making it a hassle to attack the paladin and a hassle to Not attack the paladin, he's not doing a good job as a defender.
All the PCs rushing towards the monsters instead of thinking about their positioning a little can kill. Particularly for the strikers.
Choke points can kill.
Never mix two encounters worth of monsters together; that is deadly.
Not helping the rogue set up combat advantage-friendly circumstances doesn't help.
Third, since your parties seem to be strapped for leaders (in general), then I would say fewer, farther spaced apart encounters, with safe places to short rest.
If this sort of lethality persists, you might wish to reduce the number of monsters in an encounter, or reduce their levels.
First of all, ensure everyone understands how Second Wind works, and that a Heal check from an adjacent buddy can help someone who's in negative HP.
Second, tactics are fairly significant here. If your Fighter isn't using his mark, and locking very potent enemies down with his Combat Superiority/Challenge feature, then he's doing a bad job. If your Paladin isn't marking potent foes, and making it a hassle to attack the paladin and a hassle to Not attack the paladin, he's not doing a good job as a defender.
All the PCs rushing towards the monsters instead of thinking about their positioning a little can kill. Particularly for the strikers.
Choke points can kill.
Never mix two encounters worth of monsters together; that is deadly.
Not helping the rogue set up combat advantage-friendly circumstances doesn't help.
Third, since your parties seem to be strapped for leaders (in general), then I would say fewer, farther spaced apart encounters, with safe places to short rest.
If this sort of lethality persists, you might wish to reduce the number of monsters in an encounter, or reduce their levels.