Flavor the ice cream: Put the vanilla ice cream in a stand mixer; beat with the paddle attachment on low speed until smooth, about 30 seconds. Add half each of the peanuts, peanut butter cups, chocolate-covered peanuts, peanut butter pieces and chopped cookies and mix until combined. Transfer to a container. Repeat with the chocolate ice cream and the remaining mix-ins; transfer to another container. Cover both containers and freeze until the ice cream is firm, at least 2 hours.
Make the sauce: Combine the sweetened condensed milk, chocolate, peanut butter and whole milk in a saucepan. Cook over low heat, whisking, until the chocolate melts and the sauce is smooth; keep warm.
Assemble the sundaes: Beat the heavy cream and sugar with a mixer until soft peaks form. Arrange the bananas in shallow dishes. Drizzle with some of the sauce. Add a few scoops of the ice cream, then top with peanut butter cups, more sauce, whipped cream, peanuts, chocolate-covered peanuts, peanut butter pieces and coconut.