other planes

[KARTIK]

i have a confusion. at one point it is said that when the soul leaves the body it gets another body. and on the other hand there is a description of other planes like pitra loka, deva loka. in patangali yoga sutra it is written about deva loka.i read it a long ago. its something like that deva are those beings who tried for enlightenment but didnt realised the brahman. so they will get rebirth after sometime. it is satisfacory reason. but what about our ancestors? there is a period of around 12 weeks in which a soul rests and then occupy the other body according to shree ram sharma acharya. so how can two possibilities exists at the same time. bhagwat gita also refers to the plane of ancestors and the rebirth concept at the same time. in brahadaranyaka upanishad again pitra loka is mentioned.if they are their in some plane then it means they didnt got rebirth. how can this happen?
thank you