i find teaching exam classes needs the teacher to have a clear understanding of examiners marking.
do the test yourself a few times to help you get ideas on techniques, such as timing notes for the listening , planing for writing and what to look for in reading. exam classes need to balance English skills with exam prep. I think its OK to explain grammar rules in native tounge, but be aware class time is the main speaking practice so I insist on set times when native language can't be used. higher level exams are very hard for students who think in their native language then translate, so you have to get them thinking in English. I ask students to consider class mates as all from different countries. its OK to forget words, but they need to use only English to communicate with each other, you can't set speaking homework!
you need to give timed exam practice in class, which eats in to teaching time but needs to happen. I don't know how big your classes are, but assume lots of work for you. I find giving individual homework based on personal needs is the only way if your students are older than 16, as they have such different needs.
when marking, try and categories main problems. don't just correct and grade, look at which aspect needs more work. eg note down why mistakes were made (tenses, prepositions, conditionals, links) so you can direct students to the right study to improve quickly.
likewise with writing, look at examiners bands, rather than correcting and grading - spilt the marking in to useful criteria - giving a student C tells them little, tellining them they score D for organisation and rhetoric but B for vocabulary gives them a clear view how to improve..
this year might be hard for you, but if your school does the same thing next year, it gets easier.