Baldur's Gate: Enhanced Edition

Complete the prologue.

During chapter 1, go inside the Friendly Arm Inn and recruit the two party members.

Technically can be missable if you skip this area and complete the chapter before recruiting.

Kill Carbos and Shank in Candlekeep during the prologue.

Complete Chapter 2.

Set the witch Dynaheir free from her prison.

Can be achieved through doing quests, or you can donate to temples to increase your reputation.

Complete Chapter 3.

Complete Chapter 4.

The killed creatures total counts across all party members. You can check the kill total of each party member in their statistics profile screen. It should probably come naturally without grinding for extra kills.

Side with the fishermen near Baldur's Gate. / Return Tanya's stolen property.
This quest starts by speaking to Sonner in the area North of Friendly Arm Inn. He will mention a witch affecting fishing. Go to the bridge in to Baldur's Gate and keep walking along the coast to speak to Tenya, the "Evil" Witch, and she will attack. Try not to kill her and you will get another quest to aid her. 
Depending on your choice you get the corresponding achievement.

Complete Chapter 5.

Discover who let the kobolds into Gullykin.

If you finish the Firewine Bridge and exit the dungeon from the final fight's room, you will reach a basement in Gullykin. Question the NPC there as to why it smells like kobolds.

Alternatively, you can find the same place by searching the houses in Gullykin. There is a named house with a hidden passage at the basement, behind a bookcase.

Help Abela the nymph escape.
In North Baldur's Gate behind the Palace a man named Ramazith will approach you and ask for your help. Agree and he will give you a quest to get a Nymph from a Mage named Ragefast. Ragefast can be found in his house behind the Hall of Wonders. Kill Ragefast and release the Nymph for the achievement.

Complete Chapter 6.

This must be done on the main character. Using potions such as Potion of Mind Focusing, which stack, can make it easy.

Bring Casson's body to Tremain.
North of the Hall of Wonders is a guy called Varci he will ask for your help, agree and follow him to the house. Here speak to Tremain and he will give you the quest to retrive Casson's body.

Appease the ghost in the Ulcaster ruins.
At night near near the ruins in Ulcaster you will find a ghost. Speak to him several times and he will give you a quest completed it and you will gain the achievement.

Finish the game with a party of 6 characters, where everyone is alive.

Complete the game by killing the main antagonist.

Restore Tamah to life.
She is pertified in the map to the north of Gullykin. Cast Stone to Flesh and talk to her.

Steal a telescope from the Hall of Wonders.
Speak to Brevlik in the Elfsong Tavern, East Baldur's Gate and he will give you the quest to steal the telescope. The Hall of Wonders can be found in West Baldur's Gate.

Sent Tamoko to the afterlife.
When you return to Baldur's Gate after escaping head to Sorcerous Sundries. Outside you will find Tamoko, the Cleric who attacked you with Sarevok. Be nice and agree to meet her by the Flaming Fist HQ. This can be tricky with the Flaming Fist hunting you.
When speaking to her outside the Flaming FIst HQ agree to her request and kill Cythandria.
Your final encounter with Tamoko is outside the Temple of Bhaal in the Undercity. use the following conversation options 1, 3, 2. Depending on your CHR will depend on how well it goes she will either attack you or walk away. I had CHR 16 and it took a couple of reloads to get it to work.

Send the witch Dynaheir to the afterlife.

Convinced Tamoko to aid you.
When you return to Baldur's Gate after escaping head to Sorcerous Sundries. Outside you will find Tamoko, the Cleric who attacked you with Sarevok. Be nice and agree to meet her by the Flaming Fist HQ. This can be tricky with the Flaming Fist hunting you.
When speaking to her outside the Flaming FIst HQ agree to her request and kill Cythandria.
Your final encounter with Tamoko is outside the Temple of Bhaal in the Undercity. use the following conversation options 1, 3, 2. Depending on your CHR will depend on how well it goes she will either attack you or walk away. I had CHR 16 and it took a couple of reloads to get it to work.

Side with the fishermen near Baldur's Gate. / Return Tanya's stolen property.
This quest starts by speaking to Sonner in the area North of Friendly Arm Inn. He will mention a witch affecting fishing. Go to the bridge in to Baldur's Gate and keep walking along the coast to speak to Tenya, the "Evil" Witch, and she will attack. Try not to kill her and you will get another quest to aid her. 
Depending on your choice you get the corresponding achievement.

This must be done on the main character.

The protagonist must have a lore score of 100+.

• A level 10 bard has a base lore of 100. Can be done in the base game.
• A level 10+ thief or wizard can do it on Siege of Dragonspear. They have a base lore of 30+, plus 40 lore from 25 Intelligence (use portions of Genius or Mind Focusing), plus 10 lore from 18+ Wisdom (potion of insight), plus Brevin's Quarterstaff for 10 lore, plus Cloak of Minor Arcana for 10 lore.

The easiest way is probably the following:

• Start a new Siege of Dragonspear game with a Bard with 18 Intelligence and 18 Wisdom (90 lore).
• Talk to the Flaming First Healer in the starting room and discuss about cadaverous undead.
• Buy and drink a Potion of Mind Focusing (+10 lore).

Must have a party of 6, and all PCs except for the protagonist must be dead.

Explore Durlag's Tower and defeat the evil growing within it.

Destroyed the demon Aec'Letec.
Return to Ulgoth's Beard with the Soultaker Dagger and you will be robbed of it when you enter the area. Speak to Hurgan again in the Inn and tell him what happend. He will ask you to retrive the dagger from the cult in the storehouse. Head in to the storehouse kill the cult members and the demon Aec'Letec for the achievement.

Find Baeloth the Entertainer and convince him to join your party.

Have Neera, Dorn, and Rasaad in the party at the same time. Having them as dead party members also counts.

Dealt with Korlasz, the last follower of Sarevok.

The cobalt moss can be found after you deal with the boss of the chapter. Afterwards, talk to Ammon and help her out with your signature.

Complete chapter 7.

Aquired a gold bust of yourself.

Destroyed the lich Coldhearth and his phylactery.

Delivered the amulets of his former companions to Coldhearth.

Talked Teleria into selling her golem.

Left Caelar Argent behind to guard the portal to the Prime Material Plane.