Hello everyone, please tell me how to create a template for email distribution in the builder process, a letter for the CONTACT field of the EVENT object, with an attached PDF file with a list of participants who belong to the EVENT object. The mailing condition is set only need an email alert
the scheme is given below

Hello everyone,
I have 3 custom objects. Car__c, Service__c, Action__c,
I would really like to know how to get a list of all cars where Action__c.category = 'SOME VALUE'.
Link mapping looks like this

I have 2 objects, Child__c and Parent__c. Field Parent__c->LastDate must be updated automatically every time if Child__c->Status becomes 'Finished'
Trigger looks like this

ChildObjTrigger on Child_c(before update){
        Set<Id> rcID = new Set<Id>();
        for (Child_c child : Trigger.new){
            rcID.add(child.Id);
            System.Debug('ID added to list' + child.Id);
        }

        for (Child__c child : [SELECT Id, Name FROM Child__c WHERE Parent__r.Id IN :rcID]){
            if (child.Status__c == 'Finished')
            child.Parent__r.LastDate__c = System.today();

        }
    }