How wonderful that other members of the family want to enjoy the activities that you are doing with your infant. What a great stimulator to hear other voices, see other faces, and smell other scents.
The most important part of having others enjoy the infant stimulation program is having them understand that babies enjoy extended periods of interaction. This is not a fleeting moment of play, but a focused period of stimulation.
So perhaps Grandma and Grandpa, and Aunt and Uncle, and cousins, should observe what you have been doing, understand it, perhaps read this blog, or get the book How to Have a Smarter Baby, and they will have a great education in how to get directly involved in their new family member's health, happiness, and brain development!