Don’t do anything. It is up to your ex where she lives and what she does with her time. It sounds like she benefits from the support of her parents in looking after your son. It is still early days in terms of the separation and you have years of co-parenting to get through. They will be much easier on your child if you can do so amicably.
Children are not badly affected by cv unless your son has a specific medical condition. As long as you see him regularly, as per the govt guidelines, let it go.