A mostly melee group will usually have a warrior or two, a hunter, a rogue and either a druid or another type of caster with limited Tibia Gold healing.
When you’re in a group that can’t find a healer, any healing you can get becomes that much more important.
Have anyone who can cast any healing or, failing that, who has decent bandages focus on doing that and not enter into melee unless absolutely necessary. Assign yourself and one other person to protect that healer.
The biggest problem you will have in a mostly melee group is people rushing in too quickly and aggroing more than you can handle.
Have hunters and warlocks put their pet in guard or passive mode, so they won’t run and attack any time an enemy is in range. Establish an attack pattern, having one person be the designated puller, and then have lines of defense before the healer.
Try to focus on keeping everyone together and watching each other so you can spread out the attacks on the whole group, not just on one person.
A tank is only as good as his healer, and in this case you’ll want to keep the group stronger by not sacrificing players.