Are the books in this series all connected or are they stand alone?  From the descriptions of the books they don't appear to have the same characters or storyline, but wanted to be sure.  I have several of them on my TBR and was wondering if they needed to be read in order or not.  Thanks!!

there's an ongoing backstory, and most of the characters are around in earlier and later books (there's sort of a core team, so you see all of them frequently even though the main couple changes).  so it's probably best if they're read in order, at least the ones you have.  books 4 and 6 are tied in a little more loosely with the characters not being part of the main crew so those are probably ok to skip over and come back to later, or possibly read earlier - but i'd still suggest reading book 1 first.

you really should read them in order, there is background information that comes in handy in the later books. I didn't know it was a series but i read vandas story first....when i realized it was a series i went to book one and there was a wealth of info that made vandas book seem sooo much better :)

Thanks for the info, I really appreciate it. 

Yep, best to read in order.