Complex sentence: Outgoing senators could nominate themselves for re-election--all 19 did so; the Senate could nominate a further 19 candidates; and the Dáil could nominate 38, twice the number of vacancies.
Split into simpler sentences: Outgoing senators could nominate themselves for re-election, and all 19 did so. The Senate could nominate an equal number of candidates, and the Dáil could nominate twice the number of vacancies.