Maybe they are hiding it because they know their family doesn't agree with it?
We know that many of us are in this situation, the family doesn't know about your gambling because you know that they will be angry with you. I can say this because I also know someone, because he is so addicted to gambling, he even used his family's money and he bet on his car just to get back what he lost. Of course his wife was so angry with him and he kicked him out and even his children were also angry with what he did.
Don't destroy your family just for a gambling hobby because it's not worth it. If that kind of hobby is not okay with your family, there are many others out there. If you are also having trouble stopping and that you are addicted, you can tell your family so they can help you. You have a family you can reach out to, you are not alone. Just tell them your problem so they can support you.
Very much with all you have said, Gambling have sure destroyed and separated alot of families around the world, I have a friend as well, who got separated from his family way back 2018 due to over gambling, and always using the money meant for important things in the family to gamble, at a point, the wife got tired, packed her belongings, took their only son and left, traveled to God knows where, changed her phone lines, and till today, we are yet to locate where the lady now lives with the boy, the family of the lady have refused to say anything, we have stopped searching, though, though my friend have never been himself since then, being some one who loved his son so much, today, he no longer gambles as frequent as before, Infact he has totally changed, but unfortunately, this much needed change came late rather, as he has already lost his family, most especially, his son..
Gambling is good, but should never be allowed to destroy things that are really precious to us, like myself, I gamble, but since I discovered my wife does not like it, I told her I've stopped gambling, but I still do it secretly from time to time, and I always make sure to never attempt gambling with money meant for the family.