Hi Nikola =)
If you really want to communicate with her, all you have to do is talk to her. If you want to see if she answers, then you need a digital voice recorder with usb hookup. That way you can upload your recording to the computer. We have several posts in the Ghostly Photos and EVP's forum regarding getting EVPs. Spirits communicate on frequency that is inaudible to the human ear, (most of the time, but not always.) This will be picked up by a digital voice recorder. You can also use a digital camera and ask the ghost if she would like to be in your picture, or if she minds if you take her pic. After you take a few pictures, be sure to tell her thank you. That may sound weird, since you haven't done this before, but in my opinion, it is very important and you are more likely to get results.
At this point, it's hard to say for sure whether what your brother is seeing is actually a ghost or an imprint or a bleed through. Since you or your younger children have not experienced or noticed things that are normally a sign of a haunting or spirit visitation, it's possible that it's not a ghost or a spirit. Young children are usually fairly perceptive to paranormal activity. There is the possibility of it being the spirit of the woman who lived there before, just coming back to her home for a visit.
Imprint: An intensely concentrated pocket of energy at a site where an extremely dramatic event or events have taken place with such profound impact, that those events become part of the surrounding area. Along with the imprint comes emotions; fear, joy, sadness, etc... Imprints often include images of people and/or animals. These are not earthbound spirits, but are easily mistaken for ghosts. One thing that will always set an imprint apart from a ghost is that the imprint image will never interact with us. (They're sort of like a hologram.)
2. Bleed Throughs: Relatively rare experiences in which the past and present meet with such force that they actually "bleed" into each other and become one event. Bleed throughs can also occur between the dimension of earth and the Other Side. Bleed throughs are not a visiting spirit or a haunting.
I'm not saying your house isn't haunted or has a visiting spirit from time to time. I just wanted to let you know there are other possibilties for what your brother saw and your older daughter felt. If you do decide to try and communicate with whatever it is, be careful that you don't invite anything that you don't want. Do not use a Quija board. Try just asking if there is a spirit present, if she would like to be in your photo, and see what happens. If you would care to post your orb photo, please do so. Orbs can be tricky, and can be attributed to dust, moisture, or lens flare. Bascially, when looking at an orb, you want to see if it has motion and/or illuminates on its own. Hope this helps.
Hugs,
Pate