Welcome to the board.
I am sorry you are going thru some rough times rights now.

Yes it will get better. Three is so worse than 2. When I had my son Breana got a little jealous of all the attention he was getting. I still make sure that eachone has their time with me. I treat them the same. Same punishments and all. Time outs for her are 4 minutes and Xander is 2 minutes, one minute per year of age.
Put him in some kind of punishment for talking to you that way or throwing the tantrums every time he does it. I know with Breana I had to use pepper and that solved the issue after only a few times of it. Now all I have to do is say we don't talk that way and if you keep it up I will put pepper in your mouth and she stops because she does not like it.
Good Luck.