The reason I say it appears unhealthy is because it sounds like all three of you are being put into positions you aren't comfortable or happy with, and rather than compromising are just giving into each other. And there's a difference between not talking much and flat-out refusing to communicate, and it sounds to me like your guys are refusing to communicate. Even if your dad doesn't like to talk, that doesn't mean he and your mom don't *communicate* about issues that affect their relationship. To me, a *healthy* relationship is one that includes compromise, negotiation, and communication, and in which both/all participants are generally happy and comfortable. But that's only the perspective of someone who's read your posts, and not someone who's actually living in the situation, so I may be wrong.
Me: 44, cis-het female, poly
Hubby: my husband, 42, monogamous
S2: my "attachment", male, 44, undetermined
Best Friend: male, 38, platonic; the one who keeps me sane through all this!
My daughters: Alt (age 19) and Country (age 16)
S2's sons: Spikes (age 9) and Beads (age 6)