I think the meaning of the word "equal" might also be different from one person to the next.
For instance, I say that both Sean and Ragabash are my primaries, and that they're "equal" relationships. However they are definitely different, I've been with Raga for five years and we are married and living together, I've been with Sean five months and we live in different countries.
What I mean by that is that I treat them the same, in that I treat Sean in a similar way I would have treated Raga when our relationship was the same age. Or, rather, that eventually, I want the same relationship with Sean as I have with Raga, considering him my husband and living together.
For me, calling him my secondary is not in line with the way I feel, as I feel it means he will always come after, and is more "disposable", when that's not the way it is at all. I don't have a husband and a boyfriend on the side, I have two relationships, one of which is older than the other one. Therefore, they have different dynamics. Some things are better with more time (you know each other better, you have a history, your ties are stronger), some are better at the beginning (the NRE, discovering each other), but to me in the end they're both very important to me, and I don't want to ever tell Sean "you'll always be five years behind".
Our relationship will evolve at its own pace, but I fully expect it to "catch up" and become a long term relationship, which at 5 months is a bit early to say... but I can already feel that it's going to last, just like I did with Raga at the beginning.
So I think maybe you think of equal as in "they're already both in the same 'category'" while they think of equal in the way I do, that eventually you'll all be just one member of a triad, and it won't be "a couple + a girlfriend".
Do talk to them about it to know how they feel. I don't think it's reasonable to expect you to go faster with the relationship as is natural for you, but I do believe it's fair to ask you if you have the same expectations as they do in the long term.