Hmm. Would a key line be 1. Nh8+ and if 1…Kg8, 2. Ng5 boxing black’s king into the corner, then winning one of black’s pieces and winning the game with 3 pieces to 1?
Bill Smythe
In the general case, 3 minors vs. 1 is a theoretical win. This includes BNN vs B (bishops of the same color) and BNN vs N.
In the general case, BN vs bare K is an easy win, and NN vs bare K is an easy theoretical draw.
Here is a mate in three for your amusement & as a hint (Alfred de Musset, 1851, version)
And yes, 1.Nh8! is forced. If 1.Ngf8, then 1…Ne3 (not the only drawing move) 2.Kxh2 (or 2.Bg5 Bd6 =) 2…Ng4+ followed by capture on f6 draws easily.
I think I’ve almost figured it out: 1. Rb7:
and if 1…Na6, then 2. Rd7 and 3. Nf6 mate.
or if 1…Nc6, then 2. Rd7 and 3. Nf6 mate.
or if 1…Nd7, then 2. Nc6 and 3. Nf6 mate.
or if 1…Kd8, then 2. Nf7 Kc8 3. Nd6 Kd8 4. Nf6 and 5. Rd7 mate.
But that last one is five moves, not three.
Bill Smythe
You have the idea, but are censoring a move that you assume is impossible. 
Ooh, you’re right. SPOILER ALERT!! Quote or PM to see the answer (or copy the area below and paste to a text editor):
- Rd7 wins in all variations.
Bill Smythe
Zugzwang!
This is the same Alfred de Musset who wrote On ne badine pas avec l’amour & La Confession d’un enfant du siècle
Solution to the Sobolevsky study, with commentary (in Spanish, but easily followed) based on John Nunn’s in Tactical Chess Endings, Batsford, 1981, page 6.
http://www.musicayajedrezdediez.com/partidas/2014-07-17(sobolevsky).htm