No, for a couple of reasons. First, it is insane to spend that much money on a wedding. Second, traditionally it is the bride's family that bears the wedding costs except IIRC for the after rehearsal dinner.
Kudos to the bride's family for setting a hard limit. I would do the same, maybe offer a $5-10K wedding check that can be used as they wish. From that point, I would tell the couple that extra expenses will be theirs.
Your son is, or should be, well aware that you don't have the financial resources that the bride's family apparently does. This doesn't even have to come up in the conversation.