Help(please)

Both are grammatically correct but they have different meanings. A lawyers' joke is a joke that only lawyers will find funny (I think this is what you meant to say) and a lawyer joke is a joke about lawyers.... e.g. how many lawyers does it take to change a light bulb?

And if I want to say "Sucessful wives of politicians" should I say "Sucessful politicians' wives" or "Politicians' sucessuful wives"?
Again, both are correct, but successful politicians' wives can be interpreted as the wives of successful politicians, so it is clearer to say politicians's successful wife to avoid confusion. 

Please. I need your help

Thank you

I hope that helps. Let me know if you have any questions. And by the way, the answer to the joke can be found here:

http://uncyclopedia.wikia.com/wiki/How_many_lawyers_does_it_take_to_change_a_lightbulb%3F