Firstly, I am so, so sorry that you are facing this horrendous choice op, it's not easy at all, but you're taking your whole families needs into account and being absolutely honest about it, and that's the absolute best you can do when facing two very difficult outcomes.
I haven't been through this exact situation, but two of my children have died.
My daughter was born with a condition so severe that, had I known about it, I would definitely had a TFMR, just because I love her so much, I wouldn't have wanted her to suffer. Had she lived, if I'm honest, I'm not sure how I would have coped, and it would severely have impacted the lives of my other dc. So I do understand as much as I possibly can.
You can ask at the hospital to meet your team before you go in, and discuss this with them. Tell them your wishes for the moment, but also allow yourself to change your mind when the time comes. There's no predicting what you will feel like, and you may even change your mind multiple times. They will be able to give you a good idea of what the whole birthing process will look like in your hospital, and for you specifically too.
There's no right or wrong way to do this, it's solely down to each individual, but remember that it's you that has to live through this, and live with the memories, so you are the most important person here.
If you do feel like you cannot see, or know anything, then there's always the option for the midwives to take photos, and write the sex down (most places offer a memory book or box) and then you can look at it if you ever choose to, whether it's in a week or 20 years or not all all.
Have the hospital offered you any counselling? If so it would be a very good idea to go and discuss this impartially with the counsellor too.
There are many places online for support, should you feel like you need it, as well. Please don't be afraid to reach out afterwards, I know many women in your situation don't because they feel guilt, which you absolutely shouldn't, you're making the right choices for you, and your family.
I hope the whole process is as gentle as it can possibly be on you op 💐