Thank you all so far for offering your perspectives on this issue and the advice.
I believe it might be worth adding that one of the Catholics sings in the choir. In fact, I was allowed to do so by the priest, too. I spent some time abroad and ever since I've returned, I haven't participated in the choir because it no longer feels right. I believe it makes you feel part of everything too soon. I'm going to inform my priest about my decision not to participate as long as I remain a catechumen for these reasons. Orthodoxy is not a hobby. It's not a religion where you pick what you like and disregard the rest.
Since I was absent for a while, there is a possibility that the Catholics I mentioned have converted. Yet again, this is highly unlikely. One of them was already taking communion long before I was abroad and clearly indicated he's allowed by the priest to commune even though he didn't convert and was still a member of a (non-monastic) Catholic community. However, I will of course ask these people about it again, and respectfully ask my priest how come they're allowed if they're still Catholics. My reason is this - allowing people to enjoy both worlds at the same time is counter-productive.
Basically, I believe what we have here are your average faithful Catholics enjoying Byzantine liturgics who are either oblivious to the fact that the two 'communities' are still in Schism or terribly confused by the excessive Orthodox-Catholic ecumenism that exists in my country. Just this week there is one of these ecumenical services, which I am not planning on attending. There's also a strong tendency among parishioners to condemn 'extremism' or 'integrism
' of the Orthodox type, and I've heard this condemnation straight out of the priest's mouth. What this means is a rejection of any form of traditionalism.
It's hard for me to wrap my head around all this because I don't see how a native can convert to Orthodoxy only to then join his former co-religionists again, regardless of the denomination. Clearly, there are some really liberal tendencies within the EPC. I don't care if I'm considered an extremist for saying this, but this is unfair to natives from a Catholic country who go through the pains of converting to Orthodoxy, a religion of a tiny minority. This has nothing to do with any hatred of Catholicism. I love many Catholics, but this is a matter of Orthodoxy. Economy is a good principle but doesn't apply here. I've heard Orthodox applying 'economy' to justify their having premarital sex, too.
Having said that, I do want to focus on my own conversion, and I fully understand why some say I ought to mind my own affairs. I know I have to focus on the plank in my own eye, but I don't think allowing Catholics to commune in an Orthodox church in a country with a nominally Catholic majority is 'sawdust', either.
To be continued, I guess. Let's hope I'm wrong about all this.