You say:
If someone is saved and baptized when they are young, possibly a teenager, and later in life, they say they believe in God but when asked if they believe that Jesus died for their sins so that they may have everlasting life, and they state that they don’t know, or they guess so, can a person lose their salvation?
Yes, a person can lose their salvation. The Bible tells us that when we believe the good news of the kingdom of God and the name of Jesus Christ and are baptised into his name, we are saved. But this salvation is not a final salvation — it is like someone being rescued from the jaws of a killer shark. They are saved from death at that point, but there are other dangers in life. However, if we are saved by the sacrifice of Jesus through our belief and baptism into him and we maintain that faith and loyalty to our Lord, we are given immortality at Jesus’ return to reign on the earth — at the resurrection.
We know that salvation is conditional, because the apostle Paul says in 1 Cor 9:23-27:
I do it all for the sake of the gospel, that I may share with them in its blessings. (24) Do you not know that in a race all the runners run, but only one receives the prize? So run that you may obtain it. (25) Every athlete exercises self-control in all things. They do it to receive a perishable wreath, but we an imperishable. (26) So I do not run aimlessly; I do not box as one beating the air. (27) But I discipline my body and keep it under control, lest after preaching to others I myself should be disqualified.
Other passages that demonstrate that salvation is conditional: 2 Tim 2:5; Phil 2:16; Heb 3:14; Heb 10:35-36; 2 John 1:8-9; Rev 3:11
You also say:
My husband made a point by telling me that if this is the case, then they must have not understood what they were doing when they were saved. I am worried about this person because they believe in ghosts, meeting with mediums that say they can contact loved ones, and argue that the Bible was written by men and even when translated it was translated by men, believe in reincarnation and do not believe in hell and believe that when you die, you are a spirit that is in-between planes in the sky–that people don’t always go to heaven. I am really worried about this person.
Your concerns about ghosts, contacting mediums, non-inspiration of Scripture and reincarnation, are valid concerns. However, hell is a commonly misunderstood subject. Hell is talking about the grave or oblivion.
Heaven going at death is also a commonly misunderstood subject. The Kingdom of Heaven that the Bible speaks of, is a heavenly kingdom on earth.