No Stupid Questions

Think of biweekly and biweekly as homonyms, they can mean either and you figure out the meaning through context.

Very few things happen twice a week, biweekly usually means every second week, but it's never used because fortnightly is preferred.

Others here are saying bimonthly means twice a month but I've never heard it used that way. Again, very few things happen twice a month, it's always fortnightly which is not the same. Lots of things happen every second month, "the board meets bimonthly", that means 6 times a year.

Biannual always means twice a year because what things do you do every second year?

In all cases you can use the alternative meaning like "I visit my cousin biannually" and it's not incorrect but of course "I visit my cousin every second year" avoids confusion.

we have bi like in binary(yes, no/ one week yes other no) and bi in like bisexual(atraction to 2 genders/ twice a week) i think the problem is more deep than the week

Because "weekly" is kind of a fraction (1/week), and 2/week and 1/(2week) are very different, but both can be pronounced very similarly. Read kind of like (2-week)ly and 2-(weekly). Which is why both meanings are used, so you need to use context to disambiguate, or just guess if context isn't available.

This is also the reason why in this thread people say "semiweekly" is the other option, but they don't all use the same other option. You have the same, but inverse problem there.