1. whats the big difference between europa universalis 4 common sense and crusader kings 2 horse of lords?
CK2 you manage a ruling dynasty of any christian feudal nation or christian tribe at the time (some expansions unlock new religions others new governments for example Old Gods unlocks pagans while the Republic unlocks merchant republics for you to play.) EU4 on the other hand you play as a nations where the dynasty has little affect on you since the ruler only affects the amount of monarch points you get each month and EU4 is based in the age of discovery while CK2 is based in medieval period
2. why do crusader kings 2 horse lords not have naval battles?
It is not in the game mainly because there were very few Naval battles of note at the time
3. lf l buy both charlemagne and the old gods then what year it begins?
You can choose between any of the start dates if you buy both.
4. can l choice my own capital in crusader kings 2 horse of lords and in europa universalis 4 common sense?
Yes you can in both.
5. does it say on crusader kings 2 horse lords how many population there are in the city in numbers and is it the same with europa universalis common sense?
CK2 and EU4 really don't show population since through most of the the time period that both games are based in there were little records of how large the population is. But Hoards in Horse Lords do have a basic population mechanic.
6. if l buy charlemagne and horse lords will the year still end in 1444 then if so then l should probably then play crusader kings 2 because it have longer play time? l think?
It will still end (although the end date is actual more like 1453 I think) and you could but in reality most games of CK2 last a long time so you the end date might not affect you before you get tired of your current campaign.
7. if l buy all expansions to europa universalis 4 then do l get all features and updates when playing common sense?
You get all the free features the current model the paradox uses for DLC is that Expansions unlock new features and pay for the free patch that comes out but the free patch often contains a few smaller features. But no you will not get all the features from previous expansions if you do not own them.
8. when playing a saved game in crusader kings 2 and europa universalis 4 then when an update arrived can l also get the update even if playing a loaded game?
No the update will wait till you stop playing before it loads. But updates sometimes break your game so you can roll back to the last stable patch before the update in most cases.
My advice is you watch some videos about the game to get a feel for them. To put it simple they are not for everyone. Youtuber Arumba often plays CK2 and EU4 so you might get a feel of the games from his videos link is right here:
https://www.youtube.com/channel/UCISPcad-6svNxgViVr_syvA
Also look on the forums and on the wiki's if you decide to buy the games for good spots for new players to start.