L'Evallier will not use contractions, regardless of who he speaks with. The Queen will adjust her speech depending on her audience and will use contractions if she feels it appropriate and/or is under stress (where her language has been known to go downhill as well!).
Eileen speaks as she finds and won't tone that down for anyone. She prides herself on her consistency. Reaction to her speech depends on her audience. Jenny gives as good as she gets, as does the Queen and the Witch. Brankaresh argues back but Eileen can normally out-argue him.
Reactions to speech will vary depending on the mood of your characters and their speech and style of speech will be reliant on that. So how speech is made is vitally important to help make a well rounded character.