Best interest of the child

If the parent who has maintained "primary custody" since separating, has resided at their parents house rent free, bill free, and regularity does not spend any time with the child due to long school days, and personal plans, is there a chance that the other parent could use this as evidence that perhaps the child may benefit from being in their care instead? The primary parent has no source of income, aside from child tax benefits and child support, which they often argue is not enough and demands more (even though it has been settled by the courts). When the primary parent is unavailable to care for the child, often the aunt (who also lives at the parents home) will unhappily babysit, or when grandma and grandpa aren't claiming divorce and moving out of the home they will babysit, or the school-year daycare provider will babysit.  This is not in the best interest of the child.

The household scenario is toxic and seems to be reflecting in the childs behaviour and mental stability. The other parent offers a 2 income home, a stable 8-4 work day and discipline - something that is not currently at the primary home.

Any feedback would be greatly appreciated.