How should I perform the tasleem on the fourth rakat when I join late in jamaat. Lets say on the third rakat? Do I complete it as everyone does and then do the remaining missed rakat? Do the missed rakat after the group finished and then do the complete dua including tashahhud?
You will wait for the Imam to do salaam, as soon as the Imam has said the salaam you will stand up (without doing Salaam) and pray the remaining Rakaats.
And Allah Knows Best.