Firstly I would like to point out that one or two Sucklings doesn't make marriage unlawful, rather it becomes unlawful when it is known that there was five, known/distinct sucklings. So let us assume, while still keeping in mind what I said above, that the first and last daughter of Woman B, have become haram for marriage by all 3 sons of Women A. So the Sons of Women A are the Maharim for both the first and last daughter of Women B, while this is not the case for the second daughter of Women B, so it would be ok for the sons of Women A to approach the second daughter of women B for marriage, as well as they have to follow the rules of conduct of men with strange women, since they are not her Maharim. I end mentioning the narration from the Prophet (peace and blessings be upon him):
يَحْرُمُ مِنَ الرَّضَاعَةِ مَا يَحْرُمُ مِنَ الْوِلاَدَةِ
What is unlawful by reason of consanguinity is unlawful by reason of
Lastly I would like to say that this answer is not a Fatwa, and is not intended to be such, and I ask Allah to forgive me of my mistakes, and to Guide us all.