Patrick Thomas is not David Michael's biological father.Patrick left right after David Michael was born. While Charlie, Sam, and Kristy are all relatively close in age, David Michael was a bit of a latecomer. Finally, David Michael didn't get an invite to Patrick's wedding in the Friends Forever spin-off, while his siblings did.
Watson is Emily Michelle's biological father.The whole adoption was a little fishy. It happened much more quickly than international adoptions usually do, there was no home visit from a social worker or anything, no visits by Watson and Elizabeth to Vietnam, just a "oh by the way, we're putting the kid on a plane like she's so much cargo." This all might make more sense if Emily was the result of an "indiscretion" on an Asian business trip, and Watson wasn't "adopting" her so much as he was providing the evidence for his paternity (at which point, since she's his kid, it's presumably much easier to claim her than it would be to adopt).
Stacey's diabetes stands for HIV.A life-threatening disease which made Stacey lose a lot of friends and have people scared to talk to her because they're afraid that they will catch it. The series started in the late 80s.