Before his sudden death in December at age 69, Alan Thicke laid out a living trust detailing exactly how he wanted his $14 million estate divided between his sons, Brennan, 42, Robin, 40, and Carter, 19, and his third wife, Tanya Callau, 41, in the event of his passing. But the process has turned ugly. In a legal petition obtained by Life & Style, Brennan and “Blurred Lines” singer Robin claim Tanya, a model-actress who wed Alan in 2005, is challenging Alan’s will and their prenuptial agreement. “Her demands are getting more egregious, more outrageous,” Robin and Brennan’s attorney, Alex Weingarten, tells Life & Style. “She wants more money. We had to act.” The petition states Tanya is claiming the prenup is invalid and is asking for a larger share…