Hypocritical yes - if your partners do nor share your desire that you are their one and only.
That said, I have been a member of two households composed of a male and two females. The first scenario lasted a couple of decades until his passing. The other female and I were not sexually involved with each other, but she and I had mutual interests outside of our guy. With the second, I thought I was joining a similar, but more sexually integrated configuration. It didn't work out, but not for the reason you mentioned in your question.
For me, it is a dynamic I hope to experience again some day. However, I lie somewhere along the bisexual spectrum. Definitely bi amorous. (I'm still determining the extent of my bisexuality.)
In both of the above mentioned examples, the lone male did meet my sexual needs and I felt well-loved in the group. If that had not been the case, then I would have considered it grossly unfair to have been forbidden from expanding my prospects. I would suggest that the best way to form your MFF closed triad is to make sure that you keep your girls happy. Due to your desire for exclusivity, it really does put the onus on you.