1. First, only SCEA and never heard of SCED. You definitely can't apply ED with any other schools at the same time. You most likely can't apply SCEA and other schools at the same time either but check the website descrption since it's pretty treaking;
2. I am not sure about other ivy schools, but HYP don't care if you apply early or not and my personal opinion is don't waste early on HYP and just do regular. Apply EA and ED at the same time or EA and EA at the saem time like MIT and Chicago, etc.