Could another pipeline in the TMX right of way be done by any proponent other than TMX?

This is just an administrative stay pending a motion to actually stay the judgment while the appeal is being briefed and argued. This doesn't get close to the merits of the appeal for a while

Yes. Despite the fact that Canada has statutory foundations for the ministries (this isn’t really the case in the UK or other Commonwealth realms) the legislation is set up in such a way that it defers to the Westminster practice that the composition of cabinet is the prerogative of the PM

You can just appoint the Minister of Foreign Affairs as Minister of International Development and then appoint the Secretary of State according to the Ministries and Ministers of State Act