In the original Australian version of this show, the "phony" sister lived with them for a bit, and used Julia's DNA when pressed to take the DNA test. When confronted that the test proved negative, phony sister confessed that she'd swabbed Julia while she was asleep because she figured Julia was definitely a Bechley. I don't remember the details of when Julia's mom got preggers, tho, just that she was best friends with Edie's mom and they were stereotypical "free spirits". She may have been pregnant by somebody else when she married Leon.
Also, Julia and Tim got friendlier again after Edie came out, although pretty much all they did was commiserate.