What I always say about a gaming system: "At one point it is very handy to read the rules to play the game correctly and completely."

I wonder what type of people you are playing with because after a year of weekly playing, that would mean 52 game sessions with one or more combats per session with let's assume 4 combat turns. That's about at least 156 times (if they only attack half the turns) they asked what they needed to roll to hit.

So what can you do to help your players? Ask if they have a copy of PHB, if they don't, they need to download the free PDF rules for DnD Beyond.

1. Demand players to explain Combat rules to each-other.

I would demand each player to explain one part of the combat chapter to the rest of the players. Once you have learned something yourself, by looking into it and figuring it out you will remember a lot better.

If you continue to pamper players as if they are in a video game, they have no incentive to learn the rules and they will not remember the rules themselves because they haven't made the effort to understand the mechanics.

2. Demand that each player prepares a character sheet

You can check before the session if each character sheet is complete. The most easy way is everybody to make an account on DnD Beyond and so you can see the full sheets and point errors out.

This will also force players to invest time in creating the sheet and reading the rules; or at least the class and features they are interested in.

What I always say about a gaming system: 
"At one point it is very handy to read the rules to play the game correctly and completely."

I wonder what type of people you are playing with because after a year of weekly playing, that would mean 52 game sessions with one or more combats per session with let's assume 4 combat turns. That's about at least 156 times (if they only attack half the turns) they asked what they needed to roll to hit.

So what can you do to help your players? 
Ask if they have a copy of PHB. If they don't, they need to download the free PDF rules for DnD Beyond or from WoTC's basic rules.

1. Demand players to explain Combat rules to each-other.

I would demand each player to explain one part of the combat chapter to the rest of the players. 
Once you have learned something yourself, by looking into it and figuring it out well enough to explain it to someone else, you will remember a lot better.

If you continue to pamper players, they have no incentive to learn the rules and they will not remember the rules themselves because they haven't made the effort to understand the mechanics.

2. Demand that each player prepares a character sheet

You can check before the session if each character sheet is complete. The most easy way is everybody to make an account on DnD Beyond and so you can see the full sheets and point errors out.

This will also force players to invest time in creating the sheet and reading the rules; or at least the class and features they are interested in.