What’s a fair family secret Santa arrangement?

[Dogsaresomucheasier]

I’m very happy to take part in a family secret Santa that my sister-in-law set up last year between adult siblings. I’m less happy now she has roped in the grandparents and the older children, who range from mid twenties to 16. Her children and another niece had generous, useful gifts from the grandparents throughout their time at university and it now seems mine are going to miss out on this. Grandparents health is failing and they are worrying us in many ways but they are materially well off.
Can I address this without being a complete tool?

[Spacerader]

Just say you are happy with secret Santa, but family members join at the age of 21, or whatever age everyone find suitable.

I think 16 is young, not many 16 year olds have loads of spare cash.

[Dogsaresomucheasier]

I’ve been asked about my involvement, she asked the kids (and the grandparents) themselves. It’s me that has an issue with it!

[Dogsaresomucheasier]

Student members have a part time job each and can afford to participate at this level.

[Dogsaresomucheasier]

SIL and bil are newly retired and getting used to reduced income.

[ChillyB]

I agree you need to set a membership age probably of 21 - I’d perhaps point out that the older children have benefited from gifts from everyone and the 16 year old won’t.
If the 16 year old is wanting to buy gifts (or expected to I’d say get something for her own parents and grandparents and that would suffice (or they could do a second secret Santa amongst their own family members not extended family).