Most guides only have an OUPV license (Operator of Uninspected Passenger Vessel), which is limited to 6 passengers. You'll often hear this called a "six pack" permit or license.
For parties larger than six, you might have to find a smaller partyboat that will take private charters. But the cost will be higher.
If you know that you'll have 8 or 9, it might be worth hiring a guide service with two boats and put four people on each boat.
"Decency is not news; it is buried in the obituaries --but it is a force stronger than crime" ~ Robert A. Heinlein, 1952
I can't give legal advice yet, but this site may have some of the answers you need: https://texaslawhelp.org/