1. Is it correct that the double stipulation only applies to matters of kiddushin and gittin?
2. If so, what is the source verse and how does it limit the double stipulation to only these 2 matters?
Barry Epstein, Dallas, USA
Wherever the laws of Tena'im (stipulations in a Kinyan) are in effect, double stipulations are required. This is learned from Bamidbar 32:29-30. There are certain types of sales for which the laws of Tena'im may not apply, and they do not need Tenai Kaful.
I think you are referring to the opinion cited by the Rambam and Ra'avad in Hilchos Zechiyah u'Matanah 3:8. The Rambam rejects this opinion, which differentiates between Gitin and Kidushin, and other Kinyanim (on the grounds of your question 2), while the Ra'avad explains the opinion based on logic alone.
The Ra'avad's reasoning is that if one stipulates that a sale should only take place under certain conditions, the sale certainly cannot take place against the person's will. However when it comes to Gitin and Kidushin, people do not joke around. If they even raise the possibility of giving a Get, they really mean to do so. We assume that the stipulation was not meant to be taken seriously and that the person probably wants the Get to take effect even if the stipulation was not fulfilled.