Gideon/Jerub-Baal destroyed Baal's altar in Judges 6:25
That same night the LORD said to him, "Take the second bull from your father's herd, the one seven years old. Tear down your father's altar to Baal and cut down the Asherah pole beside it.
Did Abimelech sacrifice his brothers?
Yes, it is probable.
Abimelech sacrificed Gideon's 70 sons on one stone block in an altar to Baal.
The murders were done with the help of the citizens of Shechem.
Judges 9:22 After Abimelek had governed Israel three years, 23God stirred up animosity between Abimelek and the citizens of Shechem so that they acted treacherously against Abimelek. 24God did this in order that the crime against Jerub-Baal’s seventy sons, the shedding of their blood, might be avenged on their brother Abimelek and on the citizens of Shechem, who had helped him murder his brothers.
Jamieson-Fausset-Brown Bible Commentary
Abimelech slew his brethren on one stone, either by dashing them from one rock, or sacrificing them on one stone altar, in revenge for the demolition of Baal's altar by their father. This latter view is the more probable, from the Shechemites (Jud 9:24) aiding in it.