Interesting and …funny, dream.

Did you ever read Jung's biography 'Memories, dreams, reflections' ?
He too had several dreams of secret rooms that he discovered in 'his' house.

Though here, the place is related to 'your work' it could also be understood at a symbolic level. Especially if this particular room is a 'dungeon', which is the place where the army retreats when enemies already invaded the castle. It could stand for a symbol of the center of the personnality, either that of your EGO or the SELF. 'Houses' are often a symbol of the ego.

'Discovering a new room in the house', could stand for 'opening new perspectives for your psyche', either at a psychological, spiritual, or professional level. These possibilities always pre-exist (the 'old' ornate mansion) but it can be difficult to make them become 'real' : conscious, as they are stored in the 'dusty old' unconscious.

What 'mangaroos' are, I can not tell you, you will have to give it some thinking. What do kangaroos associate with, for you ?

Half man/half human probably means that this new potential is still in a primitive form and that it still needs to evolve. This could be why the mangaroos ask for 'juice' (energy ?). Now that you have access to them you can give them some more appropiate food.

I wonder if this makes any sense with the rest of the dream ?

What aspect of the mangaroos was most noticeable (did I spell that right?) to you? I think that makes a big difference to the interpretation. For instance, if it was the tail, your beastie maybe indicating balance or a need to be rooted. If it was the pouch, you may have an idea that you need to tuck away and let it gestate, or you may need to explore your 2nd & 3rd chakras. If it was the legs, then I definitely think taking a new leap is important.

Something that stands out to me is that both "juices" have a common ingredient: alcohol. And you were disturbed because they didn't have anything else to nurture them. Does anyone you know have an alcohol problem?