I think it's actually a lot more complicated than that when one is deciding if something is a sin or not, especially when it's something that falls into a bit of a gray area.
Here are some points to consider about moral theology:
1. By taking a vaccine, are we in moral cooperation with murdering babies?
2. By taking a vaccine, are we demonstrating a material connection to evil?
3. Though we may not have been the ones to murder the babies to harvest their stem cells, does purchasing vaccine products validate and enable evil?
4. Is taking a vaccine being in agreement with murdering babies?
5. Is there a moral alternative to the vaccine? If yes, then should the vaccine still be an option?
6. If taking a vaccine is a sin, (many Christians think it is) will it create scandal within the church for church members to take it?
If it is correct to buying food and cloth from a sinner? If so then you have to produce your food and cloth from your own, but be careful not to sin.
The 2 Babys you mentioned where murdered in the 60s and 80s. Today is nothing from them in the vaccines.
People researched and cut of death bodys and could study in this way the anatomy of an human beeing. We all have benefit today from these researches.
5. there is no alternative to a vaccination. Many people had benefit from vaccines against polio, chickenpox, measeles, rabies and Hepatitis A they all based on the derivates from the above mentioned fetal cells.
Of course would be an alternative, which you can call an alternative available i would prefer this.
But to call vaccination a sin, you have to add many more a sin. We live in this world so long the Lord let us live here. We must not live like the World does, but we live in.
Btw we Christians tend to make more laws, then the Lord is given to us.