Will a court separate siblings in a custody case?

My ex-husband and I have 2 daughters, and one has special needs. He wants shared custody of both girls. He’s a good dad, and I have no problem sharing equal time with him for our older daughter. However, our special needs daughter requires a lot of time and attention, and he has never been able to properly care for her on his own, partly because he won’t acknowledge she has disabilities. We are going to court soon for custody, and I want to know whether a judge could issue two different custody arrangements for our girls – shared custody of our older daughter and primary custody of our younger child to me? Is this the type of situation where it would help to have a lawyer represent me? So far I’ve been doing it on my own.