Masa 8 bulan ada babies yang masih belum ready untuk crawl or sit up, so don't worry too much yet, setiap baby develop at their own pace! That said, a few of my mum friends had the same worry, and their pediatrician suggested doing simple exercises like tummy time and supporting baby to practice sitting, tapi best to check with your doctor just to make sure everything is on track, okay? Could be normal, could be they just need a bit more time, but worth getting peace of mind from the clinic.