S.K.
I love the two way radio idea as a first line therapy. The real issue here is that your daughter is crying out for attention and validation. You need to find ways to let her know that you value her as a companion and that she is an individual worthy of love. Then tackle the issue of attention by including her in your life. You can do things like including her in meal planning, volunteering in the community or engaging her in activities that she normally enjoys alone. It also sounds like a committment from her dad and brothers to spend one-on-one time with her would help her feel included in the family more.
I hope this helps!
S.