We've been told that someone living in your house who has access to mobile phone and pc can track all the phone calls coming into the house, could this be true?
Surely, only if they have sophisticated IT programmes. I couldn't do it. How would you track landline calls coming into the house? You'd need to have a tap on the incoming phone line (wouldn't you?).
I think whoever told you should give more details. With the right equipment one might be able to tell you had a mobile call. I do not know if digital mobile security is still secure enough to avoid tapping. It's possible control signals could be decoded. But landline needs something in the line to monitor it (or access to your account on BT or whoever). It seems rather unlikely to me, and maybe someone misunderstood what could be done, and we have a case of "Chinese Whispers".
I don't know about the phone calls but my friend's son who runs about 20 computers in his house to fix them - she believes can go into various computers if he wants to - I do always wander why she never never says too much on the emails.