Hi Darshil,
One quick update - I tested this scenario where I have placed all my required internal stakeholders email address in the "To Other emails" section of Send Alert flow step and they all recieved the email deliveries just after the "Send Email" flow step runs.

However, I have a doubt here - I imported the same email addresses(which have been blacked) and added it into list and called it in the flow;

Issue is Marketo is not considering the list calling in the flow step and only sends alert to those members who have been added in the "To Other emails":

Questions:
1. Can you please let me know how to add the distribution list email addresses as a single email address ?
2. Do we have any justifications of this behaviour as to why it is not considering the member of list condition and only sending an alert to the "To Other Emails" recipients ?
Questions:
1. Can you please let me know how to add the distribution list email addresses as a single email address ?
You need to request your IT team to create a distribution list with all the internal seed list addresses. Once that is done, you could send an email to everyone on the list by sending it to just one id set up by your IT team. e.g., marketingseedlist@<your-company-domain>.com You'd need to create a person record in Marketo DB with this distribution list email address.
2. Do we have any justifications of this behaviour as to why it is not considering the member of list condition and only sending an alert to the "To Other Emails" recipients ?
The Member of List choice step condition executes based on the person for whom the campaign flow has been executed, i.e., the person qualified for the campaign. That is, in simple words, the send alert would only be executed if and only if (iff) the person with the Email Address in campaign SL would be present in the static list mentioned in the Send Alert flow's choice step.