They feel what the adults around them condition them to feel. If the adults are worried about the child being jealous, tell the child not to be jealous and that they'll still love them just as much, and generally think negatively about it - the child will be jealous. On the other hand, if the parents are simply excited about the new addition and get the child excited about the new addition too and helping, the child will not be jealous but excited.
We have 7 children, and to my knowledge never had a problem with older children being jealous of the baby. Because we never expected it, so it didn't happen. Instead, our toddlers would come and give their most precious toys to the baby to express their love for them.
I've seen it in some of our children, not in others, and we don't do any of those things you say would trigger jealousy. Your children are not my children; which is to say different families have different tendencies.
But we know how to handle it, it wasn't bad, and was of little consequence.