As for your first question, how can anyone be happy in heaven knowing about the people in hell: they can’t. They think they can, but they’re wrong.
They think too little of themselves, and/or they have stunted imaginations. They think they will look on in approval as we’re all flung, screaming, into the flames. No. Rather, they will feel the heat, and remember some time in their own lives when they accidentally touched a hot stove top, or spilled some boiling soup on themselves, they’ll remember the horrible, astonishing pain. They’ll hear us shrieking in unimaginable agony, and smell our burning flesh. Except for the clinically psychopathic among them, they will begin falling to their knees, throwing themselves at God’s feet, begging him to stop this monstrosity, to let everyone out, to find some other way to deal with sin.
Why? Because they’re human beings, and human beings are good, in general, sometimes in spite of themselves. Their goodness will overpower them on Judgment Day. Have compassion for those who imagine you burning in Hell. Their nightmares are driven by self-loathing.
Peace and luck