Results: Stepparents ok but stepgrandparents??

I need advice!! I've help raise 4 stepchildern for 6 years. My parnter has full custody so I'm the only mother figure his kids know. He has also been the only father figure for my 2 but now that I have a grandchild he is not active at all in her life. It's to the point that he doesn't even speak to her when I babysit. She is only 6 months but still it's like shes not there. Am I wrong in thinking he should he more involved? Should their be a line with stepkids or grandkids or do you treat them like their your own? I love all kids especially babies and I'm head over heals for my granddaughter. I feel like he should be too. So what's your opion? Please comment below.