Honestly, the best thing for you to do is just smile, nod, and tell them thank you for the advice....and then let it roll right out of your head

You'll worry yourself sick if you listen to your family tell you what your child shoudl or shoudl not do.
Every baby is different, they grow at different rates and eat at their own rate. Whatever your baby is doing, and as long as your little one is happy and healthy, then I wouldn't worry about a thing