# In the meantime

"Meanwhile" or "At that time"

# they trampled on each other

"they were stepping on each other" or "they were stepping on one another's feet"

# he began to say to his disciples first of all

"Jesus first started speaking to his disciples and said to them"

# Beware of the yeast of the Pharisees, which is hypocrisy

Just as yeast spreads through a whole lump of bread dough, the hypocrisy of the Pharisees was spreading through the whole community. Alternate translation: "Guard yourself against the hypocrisy of the Pharisees, which spreads like yeast"