No one has suggested the following yet…(at least not in my brief skim through the responses)…
Why not tell your parents (or one of your parents, like your dad)? If you are indeed in a state of mortal sin and you’re receiving communion…wouldn’t it be better from an eternal perspective to tell your parents and abstain instead of adding another mortal sin on top of the pre-existing one? (Of course, it might not be mortal in your case, as others have said. Sometimes ingrained/habitual vices are not mortal because you do not have full consent to choose these actions. As others have said, talk to your confessor.)
You seem to be quite concerned about how your parents will react. I don’t know your parents, so maybe your concern is warranted. But here’s what I’ll say. I have a ton of admiration for people who abstain from communion due to mortal sin. It’s a hard, humbling thing to do. Would it be better not to be in mortal in sin the first place? Yeah, definitely. When we’re in a state of mortal sin, we need to do everything we can to get to Confession and to avoid the fault in the future, relying on the grace of God. It’s brave to admit to yourself (and others) that you are not worthy to receive at that time. (Not saying that’s the situation in your case - you may not be in a state of mortal sin, as I said. Just wanted to reiterate.)
I’d be really proud of a son who had such reverence for the Eucharist that he did not receive in a state of mortal sin. I mean, I’d definitely want him to get help for the mortal sin he’s struggling with, though. It sounds like you’re also concerned because you have younger siblings who look up to you. IMO, there’s something powerful about the witness of someone who falls and then (repeatedly) lets God pick him back up by going to Confession and resolving to sin no more, always trusting in the mercy of God and in His grace for aid in overcoming temptation. I don’t know how old your siblings are. If they’re old enough to surmise that you’re avoiding communion due to mortal sin, then you can still witness to them by letting them see you walk into the confessional. Some day one of them might struggle with some mortal sin, and your example from years before will be very powerful - the example of letting God pick you back up, trusting in His mercy and in the grace of the Sacraments Christ gave us.
Back to talking to your parents. What if chastity was something that your own father also struggled with? If you had a son who was going through what you had gone through, wouldn’t you want to help? Or if you had a son who was fighting any spiritual battle at all, wouldn’t you want to help? I’m going to make the assumption that your family is pretty devout since you’re going to daily Mass. If your parents are serious Catholics, they’re going to take their children’s spiritual growth very seriously. If they knew the struggles you’re going through, can you imagine all the extra intercessory prayer you’d be getting to overcome this? Heck, they might even start covertly fasting for you. You never know. Again, I don’t know your parents, but I think they could be very serious allies for you in this spiritual battle.