My grandma doesn't remember anything even our family members is this considered as alzheimer's disease?

Could be: Description is consistent with alzheimer's but could also be due to medication reactions, or even multiple small strokes. The diagnosis needs to be clarified, as meds are available that could help a lot, in some cases. See your doctor and get some help.

Possibly: Alzheimer's disease is the most common type of dementia. It often starts of with memory difficulties and slowly worsens to the point that other cognitive domains are affected, such as the ability to do routine things like dressing or driving. There may also be language or speech difficulties, and inability to recognize familiar people. However, other medical conditions can also mimic dementia.

Most likely: Unfortunately, not recognizing family members is quite common in advanced alzheimer's disease. It might help if you always introduce yourselves when you are visiting your grandma.