It is impossible to say over the Internet. If a baby is not regaining weight after an initial loss then it is important to look at why.
The type of birth, gestation, blood loss, underlying endocrine problems for mother, fertility treatment and much more will all have an impact.
Whether the twins were initially feeding at the breast before switching to expressed milk and when the switch happened will also affect things.
What bottles are being used.
How expressing is going and what volumes.
How long it takes the babies to feed and how much? How well they feed, do they double dribble milk for example.
In other words I would hesitate to say you have a midwife problem. Rather it is a complex issue and while there may not be any concerns with the twins or is also possible that there is. They need, if they have not already had one, a full feeding assessment which takes into account the whole story. If there is a problem then a comprehensive feeding plan needs to be implemented so that everybody knows the expectations and it needs to be a plan that is sustainable for their parents too.