For the OP . . .
MOST MOCs give at least some of their 10 noms to LOA candidates, assuming they have LOA candidates in their state/district. There are some twists to this general rule, however.
In the past, MOCs preferred to give their noms to LOA candidates b/c they knew those folks would receive appointments. At some point, however, a couple of things happened.
USNA started giving out more LOAs and, quite frankly, some of those candidates didn't interview well -- and I mean not well at all. They looked good on paper but were not impressive in person and thus the MOCs started to say -- hey, wait a minute, why should I give one of my 10 precious noms to a candidate who may have impressed USNA but doesn't impress me? So, some w/LOAs didn't get noms.
On a more clever note, some MOCs with LOA candidates said -- hey, what if I give a nom to the LOA candidate but a PRINCIPAL nom to another (non-LOA) candidate; that means I automatically get 2 appointments. Well, if you so the math, with fewer available slots due to smaller incoming classes and a decent number of MOCs getting 2 appointments (or even 4 in some years), the numbers don't add up - far too many "guaranteed" appointments and too few slots. This is largely what happened last year when a small number of principal nominees ended up w/o appointments.
So, the answer to your first question is . . . no one can tell you. In my experience, if you're a great candidate, you'll get a nom, even in a very competitive area. However, it's not a sure thing and, today, LOA recipients w/o noms typically receive TWEs.
As to your other question re 2 LOAs -- actually, if you're in a competitive district, it complicates matters. In competitive areas, most MOCs ask candidates to "pick one" SA or to rank them in terms of preference. I can only say to CHOOSE WISELY. If you are in a super-competitive area (and especially if all the MOCs are from the same political party), you may well only get one nom period. One nom to one SA.
If you rank USNA first for two MOCs and (for example) USAFA first for the third MOC, you may well only get a nom to USAFA. Great if USAFA is your first choice -- not so great if USNA is your first choice. IOW, be careful of trying to "game the system" and get two appointments -- it might happen but you also might lose out on an appointment to your first choice.
So, to answer your question, having 2 LOAs helps IF you really want to attend both schools and like them equally. That way, you can split your preference and have two shots at getting an appointment. However, if you have a clear first choice, it really doesn't help you at all b/c you should list that choice first w/all your MOCs and that puts you in the same position as if you only had one LOA.
Lengthy explanation, I know. Hope it helps.