I'm not doubting for one minute that Aer Arann are going to start flights from Glasgow in partnership with Aer Lingus but if, as you say, Aer Arann are going to pack up and leave Prestwick on May 21st then why are the Donegal flights still from Prestwick in August. Go check the web site!! I have been led to believe that the Donegal flights are not part of the Aer Lingus partnership.
Yes, the Aer Arann flights to PIK are Aer Arann's own flights. The flights to GLA are part of the new Aer Lingus partnership, so I doubt they will axe PIK just because EI fly to GLA.