My mum breastfed my baby sisters until seven months but was comp feeding from three due to low supply.
She wishes she had found a way to continue the breastfeeding as she has found bottle feeding with the girls hell, and she has two teenage boys to help her so she has had it easier than most. But it will be different ith all babies and all mummies.
If your babies come prematurely hilst it is harder to get a supply, it is important for you to keep BFing if possible. The girls had bleeds on the brain and seizures and all sorts and my mum is convinced that BFing for so long has been what has kept them healthy (they are now 12 months old). She had never successfully breastfed before so she worked really hard to make it work ith the tins.
You should get in touch with the AMBA they will probably have a lot of great resoources for you etc.

Sorry for the ramble