I am contributing to this as I am coming at it from the opposite side. I am the parent, have five adult children, three of which are always very happy to contribute towards joint presents, the other two (not particularly hard-up, but at different points in their live), always seem to resent it.
I tend to find out about these family disagreements sooner or later and it makes me very unhappy that I seem to be the cause of these.
These two are the youngest (twins), and both have good jobs, good hubbies, but young children and mortgages, etc. etc. I can quite understand and sympathise with them wanting to spend their money within their own family circle. My oldest child and his wife - both in excellent jobs - have no children, the next one down (with whom I have always been closest) is in a good financial state now (although had some very difficult times in the past as a single mother and I was able to help her out), the third is not such a good financial position, but is close to me and wants to help out.
It has made me very reluctant now to make any comment or request of any high expense items from them all. Would rather have small cheap items, or better still- visits from them.
No way would I want any of my AC to go without something themselves in order to contribute towards something for me.
The OP does need to be absolutely honest with her siblings and with her parents. I am sure they would be horrified if they found out that this was causing problems in the family. As parents, all we really want is to know that our AC and our G,children are having a good life - AND for them to keep in touch and come to visit. Not expensive gifts!!!