grammar - Double possession dilemma: should I say “your” or “yours”?

What is the best way to say this?

Because of yours and the John Wichel Foundation’s grant we are able to continue our mission to serve all Texans with diabetes.

Should it be

Because of your and John Wichel Foundation's grant, we are able . . .
OR
Because of yours and the John Wichel Foundation's grant, we are able . . .

It's a double possessive with the word your. No matter how I write it, it doesn't sound right.