In Massechet Kalla [quoted in Tosafos Kesubot 7b] we learn that we make a Brachos at a wedding [Birchos Erusin] from .... Lavan. The Haggada says that Lavan was worse than Pharoh!! How can we learn Halachot [this is not the only one] from Lavan?

It's not Lavan we learn from, it's the Torah we learn from. The fact the Torah chose to write these details in this specific way is our source to the above.