1)
What is the meaning of "v'Lo Zachru... Es Hashem...; v'Lo Asu Chesed Im Beis Yeruba'al"?
1.
Rashi: They killed his sons, like it says below (9:5).
2.
Malbim: The salvation was miraculous. They should have remembered Hashem; they did not, for they attributed it to nature and Gid'on's strength. If so, they should have remembered the good that Gid'on did for them - but they repaid evil for good.
2)
Why does it say both Yeruba'al and Gid'on? It suffices to give one name!
1.
Radak: This is to identify greatly.
2.
Malbim: This shows that they did not do Chasid with Gid'on due to being Beis Yeruba'al (quarreling with Ba'al), and they began to sacrifice to it after he died.