OP, please don't worry about offending anyone, you are in an incredibly hard and deeply distressing situation and everyone on here is supportive. I am so sorry for your pain and the impossible situation you are in.
I know someone whose baby was diagnosed with a terminal condition at the 20 week scan, but I'm afraid I can't remember the name of the condition. She was told that if her baby did make it to birth that baby would die soon after birth. She and her husband decided they wanted to continue with the pregnancy, she said her reasoning was that she wanted to give the baby as much life as it could possibly have. She said the medical staff were incredibly kind and respectful at every appointment and she was fully supported. Her baby died just moments before birth.
I also know someone whose baby was diagnosed with Trisomy at the 20 week scan, and she and her husband chose to end the pregnancy then. Both these women faced an impossible situation and made the best choices they could for themselves and their families. Both babies were dearly wanted and anticipated, and the loss of both has been profound for both women. Incidentally, both women are deeply religious and they both made their decisions within the framework of the same faith, if that is helpful to know.
I know this is not the same, but my then 2 year old son kept saying "baby in Mummy tummy" for the weeks after I miscarried our second baby. It cut me to the heart, but I realised that he must have sensed something and was trying to make sense of it and of why I was so sad.
I really hope you can come to the decision which is right for you. 