Is it possible for the Alliance Party of Northern Ireland to form a Government if they win a majority?
but representatives of minority parties would have positions in that government. The Alliance Party would lead the government and appoint a majority of ministers.
is it possible for the Alliance Party to form an executive without the Unionists and/or Nationalists if they did get enough seats to form a majority
According to http://education.niassembly.gov.uk/post_16/the_assembly_and_executive
The Executive Committee – or ‘Executive’ – is the Government of Northern Ireland, made up of Ministers in charge of Government Departments. Ministers are MLAs chosen by their parties under the D'Hondt System, which allocates seats on the Executive based on the number of seats parties win in the Assembly election. The more MLAs a party has, the more Ministers it can appoint. A special arrangement is in place to appoint the Minister for Justice, who has to be elected by the Assembly with cross-community support, ie, the support of both nationalists and unionists. In the 2011-16 mandate, four parties were entitled to seats in the Executive under d'Hondt. A Minister from a fifth party was elected as the Justice Minister. After the election of 5 May 2016, the UUP and SDLP decided not to take their seats on the Executive (they were entitled to one each) and and formed the first Official Opposition in the Assembly. The DUP had 4 Ministers and Sinn Féin had 3 Ministers. The Assembly elected an independent unionist as the Justice Minister.
So, if I understand this properly, if the alliance party did not get enough seats to form an completely overwhelming majority, one or more of the other parties would be entitled to appoint some ministers in the executive.
- There are 90 Members of the Legislative Assembly. (Source)
- There are 12 members of the executive. (Source).
So if my arithmetic and assumptions are correct, a party needs to win 90/12 = 7.5 = 8 MLAs to be sure of the right to appoint a minister. So the number of MLAs needed by the Alliance party to exclude other parties from the executive would depend on the number of other parties but I guess would be around 90 - (3 x 7) = 69?
If small minority parties are allowed by the rules to combine in some way then an overwhelming majority would be at least 90-7 = 83. I haven't read enough about NI assembly and d'Hondt to know what happens if there is a sudden (and maybe temporary) merger of convenience. It is of course fabulously improbable that, say, Sinn Féin and the DUP would merge in the event of catastrophic electoral defeat. So an effectively overwhelming majority might be smaller.
Note there are special rules for the justice minister which may invalidate this reasoning.