You have a problem if you don't tell your relatives, that is you will be asking your son to keep a family secret which will be extrememly stressfull for him. This will be even more difficult if he is staying away from home on his own and being subjected to a stringent regime that he no longer follows at home. It will become more difficult as time goes on. If he lets slip that you no longer believe then if there are consequences with your family he may blame himself.
If you can curtail the extended visits whilst you make the adjustments in your life then it will help your son. If not then you need to explain to your parents that you have regretfully decided to leave the congregation. You have given this step serious consideration and have decided that you will leave your son to make his own choices when he is old enough.
You can not prevent your family taking him to meetings, field service and study because they will see him as the way to you. If they are the staunch witnesses you indicate they are then you know that all this will continue whatever you say.
The problem as I see it will be if they know you have fallen away then they may treat you as a disfellowshipped person and not wish to see you at all. They may still wish to remain in contact with your son and therefore he would be with them unaccompanied. He will receive pressure from them to conform to JW ideals and in turn put pressure on you.
I know that there are times in the year when relatives offering extended holidays can be a blessing. I don't know if you work and use this as a childcare option in summer break, if you do it may be better to look at other alternatives. Still visit relatives but do so with your son for shorter periods. State that this year you are trying something different and feel that your son needs variety in his life as he grows older.
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