Middle name spelling (read description)

So my husband and I were talking last night about trying for baby number 3. We currently have two beautiful girls and would love to have a boy but did discuss the chances of having another girl. We talked a little about names. Both of our girls have one of our grandmothers names for a middle name and we thought that we would use both of our moms names as middle names if we have another girl. His mom is Mary and my mom is Anne and I just wasn’t sure if we merge it, hyphenate it or have her have two middle names. Just want opinions on what other mamas think!