Who are Yaakov's "brothers" mentioned here?
Seforno, Malbim: They are Lavan's "brothers" (relatives) who had come with Lavan. 2
Ha'amek Davar: They are people that Yaakov converted; they were below the mountain, and Yaakov. They spent the night in the mountain with Yaakov to protect him, for they saw Lavan's angry face; he was suspected of murder.
Sifsei Chachamim explains why above (31:46), Rashi said that "Echav" is Yaakov's sons.
It was not necessary to invite Lavan, who was like a father of Yaakov's sons (Seforno), or because he was with Yaakov, and it is as if he was the host, and Yaakov was his Shali'ach to invite everyone (Malbim).
What is "Lechem" that he called to them to eat?
Why did Yaakov slaughter for them to eat meat?
Bechor Shor: It is the way of Chasidim to make a Bris over a slaughtered animal - "Chasidai Koresei Berisi Alei Zavach" (Tehilim 50:5).
QUESTIONS ON RASHI
Rashi writes: "Yaakov slaughtered a Zevach - He slaughtered animals for a meal." What is Rashi clarifying?
Gur Aryeh: We should not interpret "Zevach" to mean that he offered sacrifices to Hashem. It would be blasphemous to allow idolaters (Lavan's men) to partake of his sacrifice.