Help Decluttering/Cleaning A Hoarding Home

Not a typical hoarding situation. My sister and I own a 3 story townhome. Depression due to our mother's passing, work/school demands, plus health struggles have gotten us to a point where we cannot tackle the overwhelming clutter and mess in our home. We need a reset to give a clean slate. Thrash thrown out, house scrubbed, clutter removed, or organized.  We can maintain once it's clean, but we can't get our arms around it because it's grown too big for us to do on our own. We need advice on how to better organize what we will keep, as storage is limited.