1). Coaliton government is legal and has always been. It is aprt of the machinery.
2). Anyone representing anything can take a seat in parliament if he/she can get the votes. It is totally legitimate for separatists to sit in parliament. The Canadian parliamentary system is based on the Westminster system and many members have been elected to Westminster who are pledged to break up the UK as it currently stands (including some such as the IRA man Gerry Adams who I consider a disgusting germ and terrorist). At least 5 members of Sinn Fein, the political arm of the IRA terrorist group, have been elected to Westminster. The Irish Republican Bernadette Devlin sat in Westminster as an Independent where she tried to physically beat up the Home Secretary. The Scottish Nationalist Party, is 100% dedicated to the break up if the UK, but has held a number of seats in Westminster and the European parliament.

It's an odd system, but it has worked for a very long time.