I am trying to pass an opportunity record collection from a flow into an Apex Action that will loop through the opportunity record collection (LIST), then create an opportunity team member record for each opportunity in that list, then return the new list as a new opportunity team member collection that will be an output variable accessable via the flow.  However, I keep getting the following errors that I cannot resolve.  I am new to Apex so I am guessing that my MAP setup is wrong.

Illegal assignment from List<Opportunity> to List<OpportunityService1.ReturnVariables>

Illegal assignment from OpportunityTeamMember to OpportunityService1.ReturnVariables

//invocable method to create OpportunityTeamMember records from a list of Opportunity Ids
    @InvocableMethod(label='Create OTM Records for OOO' description='Given a list of Opportunity IDs, create OTM records from these IDs.')
        public static List<ListReturnVariables> createOTMRecords(List<InputVariables> inputVariables) {

            //inputs
            List<Opportunity> opps = inputVariables.get(0).opportunities;
            String varUserId;
            

            //outputs       
            
            Map<Id, Opportunity> opp = new Map<Id, Opportunity>(opps);
            List<ReturnVariables> OTMOutputs =[SELECT Id FROM Opportunity WHERE Id IN: opp.keySet()];
            for(Opportunity o : opp.values()){
            ReturnVariables otm = new OpportunityTeamMember(OpportunityId = o.Id, UserId = varUserId, OpportunityAccessLevel = 'Edit',TeamMemberRole = 'Mortgage Banker');
                OTMOutputs.add(otm);
            }
            return OTMOutputs;
        }
        public class InputVariables {
            @InvocableVariable
            public List <Opportunity> opportunities;

            @InvocableVariable
            public String varUserId;
        }
        public class ReturnVariables {
            @InvocableVariable
            public List <OpportunityTeamMember> OTMOutputs;
        }