Assuming everyone survived in Mass Effect 2, where and how do they make an appearance?

Solution 1:

Be warned; spoilers follow...

• Kaidan or Ash shows up at the end of the first mission. They will be unavailable to the party for a while. They can possibly die, or re-join the party later on.

• Liara joins the party on Mars.

• Garrus shows up when you go to rescue the Turian leader and joins your party

• Kasumi shows up when you agree to help a fellow Specter investigate a Hanar diplomat on the Citadel. When the mission ends, she can join up as a war asset.

• Thane is in the hospital on the Citadel. He cannot join your mission since his condition is terminal.

• Miranda will communicate with you several times, and meet up on the citadel. You will later encounter her on a mission where it is possible for her to die. If she survives she will become a war asset.

• Zaeed can be found on the Citadel while investigating the Volus ambassador. This quest is triggered after the Cerberus attack on the Citadel. He can join up as a war asset.

• Wrex, shows up at the summit between the alien leaders after you retrieve the Turian patriarch. He stays on the Normandy, but he does not join your party.

• Mordin can be found on the mission to rescue the Krogan Females. He will come aboard the Normandy, but he won't join your party.

• Grunt is found on a mission from Wrex to rescue some Krogan scouts. He can join up as a war asset.

  Jack shows up during the rescue mission to the Grissom Academy. She may join up as a war asset, and you can later talk to her at the night club on the Citadel.

• Jacob is found in the mission to retrieve some Cerberus scientist that is triggered after the attack on the Citadel. He can join up as a war asset and can be talked to at the Hospital.

• Samara is found in the mission to investigate an Asari colony that is triggered after the attack on the Citadel. She can join up as a war asset and can be talked on the Citadel

• Tali and Legion are both found in the mission to recruit the Quarian fleet. Tali can join your team, but what happens to Legion is very dependent on player choice.

• During the end game you will have the opportunity to speak with all your surviving squad mates past and present one last time.

Some other Normandy crew non-squad mates show up as well.

• Dr. Chakwas can be found in the Citadel hospital and can re-join the crew.

• The two Normandy engineers from ME2 can be pardoned in the Spectre office, and will rejoin the crew.

• Kelly Chambers can be found in the refugee camp on the Citadel. She won't join your crew. You should also convince her to go into hiding or she'll get assassinated by Cerberus operatives when they attack the Citadel. She can also be romanced.

At the end of the game you will be able to communicate with all of your surviving squad mates before the final mission.

Here's some information to help with keeping your team mates alive.