As it is a city park approval from the city may be required contact the special events department for Houston
I believe you can, but it sounds like you may need to ask if it is okay since this will be for free, and for all to see.
As long as you don't exceed the "no more than 10 people" i think you should be good but if you are asking in general where like everybody can watch. I believe it will not be allowed. The most number of people i've seen gather was for a family picture and there was about 10-12 of them including the photographer and his assistant
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