When the Sage of the six paths i.e. Hagoromo and his brother Hamura defeated the juubi.
Is it that after defeating the Jubbi, Hagoromo himself sealed the whole juubi?
If Hamura sealed a part of the juubi inside him too, does it mean that we haven't seen the full power of the juubi in the battle?
A couple of things to explain your question. Hamura never sealed any part of the juubi in himself, he was sealed entirely in hagoromo. Also, I don't know if you're talking about the anime or the manga. If anime, no, you haven't seen the full power of the juubi yet, as the resurrection was incomplete due to lack of the hachibi and kyuubi. In the manga, its full power is shown.
Hagomoro split the ten tails to 9 individual tailed beasts, while the juubi body is trapped into the moon. Thus when all the tailed beast are combined, the full power is obtained. Hamura did not seal any parts of the beast.
