Re: Ghosts
LOL ^
Its like my cousin who lives alone at Uni. He said he saw paranormal activity once alone in his flat, never slept alone in the room normally after that :D
aap ko dara raha ho ga k kahi aap us k guest na ban jain :)
Re: Ghosts
Uhuh 
I’m a cynic, so maybe that you and your sisters saw was not your mom per se, but probably your image of her, your desire to hold on to her and see her once again. Siblings are siblings for a reason and the relationship between a mother and the kids is IMO one of the strongest, and considering the prolonged illness your mom had, no wonder you guys wanted to see her.
As for concept of ghosts/spirits in Islam, as to my knowledge, there isn’t any. Yes there is a concept of Jinn, like you mentioned, and belief is that all sorts of mischief we percieve is their work, but souls probably have better things to do than return back to us. As for seeing a dead one in our dreams, the thought is that it probably means the soul is unhappy at the moment, so you should probably recite some surahs to ease the soul and bring them to peace.