I secretly take days off work
Why would you do that?
Because I like to spend more time at home with my family.
If you are staying home from work to be with your family, you can expect to get into trouble with your boss. If you really care about your family, you should balance your time so that you can be with them, but also keep working hard to maintain your steady employment.
But I'm the only engineer in a company and the only one who has a degree.
In that case, it sounds like you are pretty essential to your company, and that might be why they have overlooked your absence in the past.  If this is the case, then I'm sure that you could work out a more flexible schedule that would satisfy your bosses and allow you to spend more time with your family.  That way, you don't have to be dishonest and risk termination.