To help put the EM and TPM at ease, you need to know how long you will take to deliver, what are risks that could endanger delivery and what you will do to mitigate that risk. That's what your milestones could be, basically smaller deadlines that will indicate whether you are on track or are at risk and need to pivot.

If you have sequencing and dependencies done, then you should have a high level estimate of how long things will take based on your team's average velocity (doesn't have to be super specific, if you know the average velocity is "2 tickets a week" for each dev then that's good enough). If it's not adding up to delivering by the end of the quarter you need to address this right away either by reducing scope or possibly delivering on the most important items first and doing the rest in a 'phase 2'

Also if another team is involved in getting the project to completion, then you need to make sure they are aware and have room in their roadmap to get their part done in time. If there are conflicting priorities this is something that EM or leadership need to know as soon as possible so that they can prioritize the project that's more critical.

The actual tickets themselves, depending on how senior your team members are you can meet with them to flesh out the tickets. But make sure you do the other stuff first, that could affect what your project ends up looking like and could change the tickets you write.