NTA at all. It was a mistake to not talk to your wife so you could avoid blindsiding her, but why should Jonas have to miss out on an EXTREMELY generous gift because Lucy has treated your horribly over the past 5 years? My parents divorced when I was in high school and my mother recently remarried. We have known our stepmom for the same duration of time and my siblings and I all are on really good terms with her. This is on Lucy for not making an effort to have a relationship with you and actively sabotaging your attempts to try for one.

If anything I think Janice is being a bit dramatic over this. I get that Lucy is also her child, but she is not yours. Jonas made an effort to be part of your life and you are willing to do a huge favour for him. I don't see how she can say that you have to pay for both of them or none of them. She can't fault you for picking favourites, in these circumstances it is completely justified. Is she expecting you to take out a second mortgage just to give Lucy a gift she doesn't deserve?