1)
What exactly, was the gist of Rachel and Le'ah's response?
1.
Seforno: They were expressing surprise that Ya'akov could for one moment think that it was hard for them to leave their father. 1
1
As they go on to explain.
2)
Why did Rachel answer first, before her older sister?
1.
Tosfos ha'Shalem (2): She was his primary wife. 1
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This is why Yakov called to her first. And even so, one opinion in Bereishis Rabah (74:4) says that she died before Leah for answering first!
3)
What does it mean "do we still have a portion and inheritance in our father's house?!"
1.
Tosfos ha'Shalem (2): Now Lavan has sons, so we will not inherit anything.