And the sons
ben  (bane)
a son (as a builder of the family name), in the widest sense (of literal and figurative relationship, including grandson, subject, nation, quality or condition, etc.
of Aaron
'Aharown  (a-har-one')
Aharon, the brother of Moses -- Aaron.
the priests
kohen  (ko-hane')
literally, one officiating, a priest; also (by courtesy) an acting priest (although a layman) -- chief ruler, own, priest, prince, principal officer.
shall blow
taqa`  (taw-kah')
to clatter, i.e. slap (the hands together), clang (an instrument); by analogy, to drive (a nail or tent-pin, a dart, etc.); by implication, to become bondsman by handclasping)
with the trumpets
chatsotsrah  (khats-o-tser-aw')
a trumpet (from its sundered or quavering note) -- trumpet(-er).
and they shall be to you for an ordinance
chuqqah  (khook-kaw')
appointed, custom, manner, ordinance, site, statute.
for ever
`owlam  (o-lawm')
concealed, i.e. the vanishing point; generally, time out of mind (past or future), i.e. (practically) eternity; frequentatively, adverbial (especially with prepositional prefix) always
throughout your generations
dowr  (dore)
a revolution of time, i.e. an age or generation; also a dwelling -- age, evermore, generation, (n-)ever, posterity.