Neurologist advice

My 14 month old is seeing a neurologist today because he isn't getting himself into sitting position from laying down, isn't pulling up correctly, can't stand independently, can't crawl, get onto hands and knees, or obviously walk (he butt scoots) . Sometimes he tips over randomly. Physical therapy says he has very low tone and is double jointed so his hips are popping out when he tries to get onto his knees. They want us to follow up with thr neurologist just to rule out any other causes for his gross motor delays.

Has anyone else gone with their baby for gross motor? What did they do at your first appointment? And were there any questions you think I should be asking (I have a list but want to make sure I cover everything)

Thanks!