As a Catholic, you can, in a sense, disagree with whatever you want, but you are bound to do your best to find out the truth if there are things you have doubts about.
You say that you were concerned with the idea of Catholics having to trust the Church absolutely. Well, presumably you’ve decided for various reasons that you agree that the Catholic Church is the Church which was founded by Christ Himself. Believing in the teachings of the Church naturally follows from this because we believe that Christ promised that the Holy Spirit would guide it and that the gates of hell would never prevail against it.
I would advise you to ask questions to get clarification on issues that you find difficult - and indeed many of the Church’s teachings are hard to take. You don’t have to settle for the “because the Church says so” answer to your questions about the faith. I have found this myself - when you have a question about a teaching, research it: it may have its origin in Scripture, which will be plain to see, or it may be a part of Sacred Tradition and you may find evidence of ancient Church teaching by examining the writings of the Early Church Fathers. Don’t forget to keep a copy of the Catechism to hand - it is the best guide to Catholic teachings, and there are excellent cross-references to Scripture, Church Fathers, various Councils, Papal Encyclicals, etc.
As for your fellow RCIA members:
Who doesn’t believe in hell: to what extent? Do they deny any sort of punishment in the afterlife for those who don’t obey the Commandments? If so, this is absolutely at odds with both Scripture and the ancient teaching of the Church. The Catechism says that “the teaching of the Church affirms the existence of hell and its eternity…” (CCC 1035). Hell’s existence is not up for discussion. However, what your friend could have a difficulty with is what the exact punishment that hell will involve. The Catechism says that the “chief punishment of hell is eternal separation from God…” (1035) - so while it acknowledges that Christ referred to “eternal fire”, the Catechism does not compel you to believe that they suffer in a literal fire - this may be the case, but Scripture does give other descriptions of hell apart from fire.
The one who believes that people do not have free will: this sounds to me that the difficulty is not free will exclusively, but a difficulty understanding how God can already know who will end up in Heaven and hell and that at the same time, people are said to have free will. The first thing to say is that God, being “outside” of time, sees our lives, all we do, and the choices we make at once. We, on the other hand, see a series of events. He sees our death as he sees our birth - at one and the same time. One cannot deny that we can make a conscious decision to do good, or we can make a conscious decision to do evil. As the Catechism says, “God willed that man should be left in the hand of his own counsel, so that he might of his own accord seek his Creator and freely attain his full and blessed perfection by cleaving to him.” (CCC 1730)
We do not know the fate of aborted babies. One hopes that these innocent children will be brought to Heaven, but the official teaching of the Church concerning unbaptised babies (including those who die through abortion) is that we can only entrust them to the mercy of God (CCC 1261). In reality, this is what is done for every person who has died - they are entrusted to God’s mercy. Beyond that is speculation, which may not be a safe route to take.
The only people we can be sure are in Heaven are those who have been declared blessed or saints by the Church. Such declarations only come about after lengthy investigation and one or more authenticated miracles. So apart from these people, it is unwise to make assumptions about their fate, but in the hope that they are on their way to Heaven (i.e. in Purgatory), we should offer prayers for their souls.
I hope this helps somewhat.