May I start with a "technical" comment? It is to be preferred that you answer questions, not add the requested information retrospectively to your original post: this makes questions for further information look silly.
New information now is - the Gerber sisters were born in canton Bern. The Register of Swiss Surnames (https://hls-dhs-dss.ch/famn/index.php?lg=e
) tells us that Gerber have held citizenship there in
Langnau im Emmental
Röthenbach im Emmental
You could try to contact the Civil Registration Offices responsible for these communities ... I am not going to predict whether they are all willing to check if they have Anna and Maria on their registers, unless you ask for a "Familienschein" - which may become very expensive with that many communities.
One way to continue is to search for additional information on your side of the Atlantic, to reduce the number of "potential" places of citizenship.
On the other hand there are already discussions on 14 of these 26 lines on https://www.geneal-forum.com/
, i.e. a fair number of Swiss Gerber researchers read this forum. If you post a query there, you just might be lucky and one of them recognizes your family. Do not "answer" to any of these topics (related to one line specifically) but start a new topic "Gerber in Kanton Bern" ... English is fine on the forum ... and make sure you give ALL the info you have, do not add small bits and pieces after being asked for it ;-).