Yes, take professional advice.
In general, bequests of specific assets — usually land — take precedence over bequests of a stated value, which in turn are paid out before residual bequests.
So, the will says "I leave my farm blackacre to my son A, the sum of €250,000 to my son B and the rest of my estate to my son C". The estate consists of Blackacre; farm machinery and livestock with a value of €50,000 and investments with a value of €100,000. A gets Blackacre; B gets €150,000, which includes the sale proceeds of the stock and machinery (or he can get the stock and machinery itself), and C gets nothing.