ubiq: You’re wrong on multiple items you mentioned including regarding whether as a practical matter we follow Hilchos Yerusha today. We absolutely do. The b’chor will as a general rule get a double portion. And Rabbonim for the most part do not recommend changing from the Torah’s Laws on yerusha. In fact, it is a major shaila whether it is even permissible. (Some hold it is.)
And Sephardim do Yibum.