We only want Salesforce to handle merging leads and de-duplicating records. We recently had an error where one individual shared the same email as another and because Marketo only uses the email field it merged and changed these contact records. This problem occurs because we often have parents using their personal email, but filling out forms pretending to be their children.
Is it possible to turn off Marketo's automatic new lead email merge?
I don't want to upload to Salesforce first either... In some cases we are forced to upload a list directly to Marketo, or these users come in through a form. I know that a Salesforce upload would mean we do not encounter this problem.
It sounds like you may need additional deduplication rules enabled in your instance. You can request for additional rules to be put in place for form fillouts so that parents would be able to create separate records for their children while using the same email address. You'll want to work with Support for that.
Yes, you will need to speak with Support as this is native Marketo functionality.
I suggest you discuss with support and any consultants you have.
This is not exactly what you are looking forward, but has been helpful for me in the past