Two Questions

1- It is possible to control other character in only 1 objective?
ex: i want to control Lisa Simpson in level 1 mission 0 , but only in a specific objective
2-How to talk to a character (ex: Lisa talking to Marge) but you go to the later objective instantly? (like in Seaside Update L3 M1, when you talk to the nerd) 

1. This isn't possible. The character you play as for a Level is controlled by AddCharacter in the Level's leveli.mfk. You change this to be a different character (such as Lisa Simpson by changing ""homer","homer"" to ""lisa","lisa""), but there isn't a way to change the character mid-objective. Sorry about that! That would definitely be pretty cool though, and you know we'd abuse the heck out of it in Donut Mod.

2. Not too hard. The first thing you need to is add SetFadeOut(1.0); or use SetIrisWipe(0.1); to the stage before the stage you want to teleport in. Once you do this, in the next stage, add "AddStageCharacter("characternamehere","character_locator","","current","car_locator");". If this is in a stage, the game will instantly teleport the player to the area defined by the locators. Do keep in mind the place you're teleporting to has to be somewhere somewhat close by otherwise the regions won't load. In short, you can't have Homer say at the school, and then teleport him to the Power Plant. The regions won't load otherwise.

Let's say for instance you want Homer to talk to the Squeaky Voiced Teen, and then after he's done with that, he instantly teleports to the Grocery Store with the car in the parking lot. Your stage would look something like this:

AddStage(1);
   SetHUDIcon("male2");
   SetStageMessageIndex(6);
      AddObjective("talkto");
         AddNPC("svt","svt_place");
         SetTalkToTarget("svt",0,0);
      CloseObjective();
   SetFadeOut(1.0);CloseStage();

AddStage(1);   
   SetStageMessageIndex(7);
   AddStageCharacter("homer","homer_teleport","","current","homer_car_teleport");
   AddObjective("getin");
   SetObjTargetVehicle("current");
   CloseObjective();
CloseStage();

AddStageCharacter expects what character you're playing as in the first arguement ("homer), where your character will be warped to ("homer_teleport"), the third set of quotation marks is always left blank by Radical and should not be touched (""), the fourth follows a similar set of rules ("current), and the last one determines where your car is placed ("homer_car_teleport).

I hope that helps.

1- :( , u.u  , thinking in Using Lisa in a Race against Homer , Bart & Marge, and then Control Homer Again (well , i would need to think of another thing
2- Thanks