The same as when they don't, of course. The law doesn't change. Which particular laws apply might.
You should ask a (much) more specific question, or even better consult a lawyer to get specific details about the particular situation you're interested in.
unfortunately, not the parents.
Since you have British citizenship, for an unlimited period of time.
The child will have dual citizenship in Canada and America. It depends on why the couple was in Germany. If he was stationed there for military reasons, the child will have no type of German citizenship.
Yes you can do it.
Yes, the child can hold dual citizenship. You just need to contact the US embassy or consulate general and get a registration of birth abroad.
In 1964 Dual citizenship is severely restricted in Malta therefore the previous births will follow that rules and must have not the dual citizenship, it would be the American. In 1989 when the Malta citizenship became allowed at birth then again it was only to those infants whose parents have Maltian citizenship or born in Malta, So in both situation they do not allow dual citizenship to a baby for American couple.
The US recognizes dual citizenship.
No. The spouse would have to naturalize in France to become a french citizen. Children of this couple, who are born in the US, are dual French-US citizens at birth. The process for "recognizing" french citizenship is complicated, however.
India does not allow dual citizenship.
Yes, Thailand allows dual citizenship.
Yes, Poland allows dual citizenship.
Yes, Venezuela allows dual citizenship.