Yes, it is possible to create a meeting link where the users don't have to wait for the creator of the meeting to join and they can join automatically. You can set the "Who can bypass the lobby?" meeting policy/setting to "Everyone" in the Teams meeting settings.
As for your second question, it is possible to create the ACS credentials for the receptionist and use them to create the meeting link. This way, the receptionist will become the owner of the meeting and will be able to join the meeting without any issues. You can use the CommunicationIdentityClient to create the ACS credentials for the receptionist and then use the onlineMeetings endpoint to create the meeting link.
Here is an example of how you can create the ACS credentials for the receptionist:
const identityClient = new CommunicationIdentityClient(connectionString);
const tokenCredential = await identityClient.createTokenCredential();
And here is an example of how you can create the meeting link:
const onlineMeetingsClient = new OnlineMeetingsClient(tokenCredential);
const meeting = await onlineMeetingsClient.createMeeting();
const joinUrl = meeting.joinWebUrl;
You can then use the joinUrl to join the meeting.
Please let me know if you have any other questions or if there is anything else I can help you with.