Well your characters are personable and memorable but this is not the best submission your made. This one's gonna be harsh but I only did it cause I care enough to see you do better with it.
One issue is that you seem to be overly fond of the word royal and might actually have confused yourself about it's meaning. It crops up far too often where other less charged terms would not only suffice they would improve the story.
Now some issues with etiquette. This is your world and the rules are yours, but people with even a little experience with a caste system will find you're world unrealistic to the point of distracting from the story.
"Tul had corrected him numerous times already on that one but Garrik knew it would take time to dispense with titles when he was around
royal blood."
How is a mere guard captain, even in the royal guard, royal blood?
"Rose petals were strewn about the path as they neared the manor, an indication that the royal line was in fact here in the manor."
The entire line? Uncles nieces cousins brother and sisters all under the one roof? Every Duke and Duchess and all their relations? Seems a little crowded to me.
The feminist slant is a bit too far for realism:
"The Sergeant was an attractive woman, not much older than Garrik."
Seargeant Jora is a problem. This is personal, but in a world of 4 lb swords and 60-80 lb armor not too many pretty women gonna be soldiers. Unless Garrik has a fetish. . . Maybe these aren't humans?
"She was in her later years but she moved quick and had a strength that surprised Garrik."
He's not surprised by a beauty in armor but a house keeper with some muscle is startling?
A few problems with characterization:
"Mirium said the last word so that it sounded like a barb rather than a title."
Servants are awfully uppity in this here King's rule!
“I suppose you didn’t count on seeing this much of him,” Garrik bit his tongue but the quip had already made it out. He cursed under his breath and tried to salvage the situation. “I’m sorry. I’m happy to have you here and glad a lady, beautiful as yourself, could join me for my bath.”
For a commoner he is certainly comfortable. I know he's stumbling over his tongue, but that's because he's attracted and naked. He clearly is not the least intimidated by a woman who is one step below the king. Wasn't he just a commoner thief 8 hours ago?
"His friend was dressed in
royal clothing for the first time in his life."
Well I should hope so! How many common thieves dress like princes? Maybe he should think of this as Fine clothing or Noble clothing?
"Dren sat down beside the blonde girl and immediately began small talk."
Why is dren even here? I can't imagine that the Talonguard would have brought a common thief into the palace and dressed him for a state dinner. Even if he WAS a companion of the new, and I might add un-invested, prince.
"Tul offered some etiquette advice as they ate."
Mere guard captain at the table with the prince AND a duchess?
Another problem is the frequent use of passive voice or language that verges very close to it:
"Inside the gate, Garrik noticed there was plenty of land to cover
before the manor itself was reached."
this is passive voice.
"The room was filled with tables at which sat more
royal blood than Garrik had ever seen in one location at one time."
Passive voice and there's that word royal again. I could forgive you the term royal if it wasn't royal blood again.
And:
"One thing you did learn growing up on the streets was whether or not you were being had and Celeste made him feel as if he were."
hrmmmm?
You might need to read up a bit on nobility and royalty in Europe. Get a feel for the historical precedents. Overall it was a bit like an SCA function where everyone acts like a landed noble and the common soldiers like knights or innkeepers all behave like barons and call one another Lord.