CTL: Mazal Tov and may the chupa take place bshah tovah umitzlachas. and bezras hashem thhat youand
Mrs, CTL should see all your einiklach get married.
1. Do I tell my son and daughter in law about this call?
Ask your Rov for guidance. It may be a shailoh of loshon harah.
2. Is this an indication that the prospective in laws expect grandparents to support married children and grandchildren?
Parents and grandparents
3. Was the prospective grand father in law out of line in making the request?
IMHO, yes.
4. Is this a new custom or a custom in communities in which I don’t live?
This is a phenomenon that shaddchanim are dealing with on a constant basis, grandparents being actively involved in their grandchildrens shidduchim.
5. If I pay for this am I expected to do the same for all my other grandchildren?
Probably.