To help eliminate your dyslexic player's issues with reading a character sheet, you might try making a "homebrew" stripped-down character sheet with more imagery and iconography than words. For instance, a humanoid shape with notations of the weapons the character is carrying near the hand that is carrying it, and a big number on the chest to denote AC or health. This would help the player to make a better association between the pure data a character sheet represents and the in-game information it corresponds to.
In addition (as Tom Bonner has noted), giving descriptive and contextual names to areas and items can help eliminate the barrier that written word presents. Calling a cave town "Dark Rock Village" or giving the town butcher the last name "Meet" might help.
As far as the issues your autistic player has with focus and concentration, it may be helpful to review tactics that teachers of autistic students use in classes, such as those given here. Structure your gaming sessions well, so they can be used to the pattern. Utilizing multimedia may help improve focus; play the same (quiet!) music every time the party enters a town, for instance, or when they go in to battle. Make an NPC's clues to the party into a song. Have props on hand for someone who can better visualize things by touch than visually.
Incidentally, I don't think that any of these things would impede your non-dyslexic or non-Autistic players. It seems to me that these are all additions that could improve any GM's game, whether they have dyslexia or autism or neither condition.
Someone has to take the player who invited his girlfriend aside and talk to him one-on-one. (I'll address that to "you", for the moment, since I hope you'll get your GM to read this.)
Make it clear that it was OK to bring her, but not OK to turn game sessions into makeout sessions. Then lay down the unfortunate reality of the situation: if they can't cut it out, then one or both of them will be firmly uninvited, and soon.
When you do this, take care to not shame them for the makeouts (there's enough shaming around this stuff in life; no need to add to it), emphasising instead that it's just a poor choice of circumstances. Focus on how disruptive it is to the game people came for, and if you mention how it makes the group uncomfortable, soften that by emphasising that there's nothing wrong with a makeout itself — just the choice of time and place. Even better, congratulate them for their obvious happiness while asking them to save it for later or take it elsewhere.
There's a consent line they're crossing here too: by joining an intimate gathering and making out during it, they're making you all surprise visual and audio participants in this overtly sexual activity. That's super not cool, and not something anyone is obligated to be okay with. Again, not something to shame them for—the point here is that being not OK with this at the table is totally justified.
When you're not the GM or venue host, your option is slightly different: go to the GM, and have them do the one-on-one conversation and ultimatum instead.
If they won't, then you present them with your own unfortunate reality: this is not OK, and you will not be coming to the game anymore if the GM/host is unwilling to enforce reasonable social boundaries during their game / in their home.
Leaving sucks, but if the GM/host is going to abdicate their responsibility to make game sessions safe social spaces, then your most powerful tool for creating change is to enforce your own side of the social contract and exercise your right to leave. Chances are that if you have to go to that degree of effort, suddenly the GM/host will realise that they have imminent group destruction on their hands and will do the reasonable, pro-social thing of dealing with the offending people. (And if they won't, you've dodged a really nasty bullet!)
The alternative — staying anyway and hoping it will just get better — will most likely result in the group dissolving anyway. Either the players cut it out, or other players will start leaving after they become too uncomfortable. The sooner you present the ultimatum of "fix it or I walk", the more likely there will still be a group to fix when you give the ultimatum.
Oh, and as an illustrative aside: I have been that player who brought his girlfriend, and was stupid about overt makeouts. That group dissolved shortly after, and though we were all friends we soon drifted apart. Let my experience be your cautionary tale!
Best Answer
I've had player conflict from time to time. Sometimes it can be handled simply, by talking to them. Be direct - as the GM, you're the leader, and it's your game. "Your fighting makes everyone else not have a good time. I'm the GM, and I'm telling you now to shape up and not bring your beefs into the game."
Look for opportunities to have them play in different games. Most groups I'm in end up having several concurrent games going on on different days or whatever, so people can stay "in the group" but not play with people that bug them. Once, to accommodate differing play styles among the group, I split the campaign and ran two different games on two different days for the two different groups.
Also, sometimes you can address it in game. I had a player who I nearly kicked out, because he would throw fits that were arguably in character but really boiled over to out of character very quickly. (This one time, he was so agitated at the group not taking the thousands of copper pieces from a dead orc tribe that after a screaming fit he just ran into a wraith and suicided.) I ended up giving him a reason to subtly spy on the other players and that sublimated his desire for conflict in a way that didn't have negative group consequences. Perhaps there's ways to sublimate their conflict in the same way. If you disallow table talk, for example, they will have to communicate in character, and arguments in character tend to get you ambushed by bad guys, tossed in dungeons, etc.
In the end, you may have to eject one or both players from your group. Geeks tend to Marty McFly about this too much and not address problems directly, read the Five Geek Social Fallacies for some insight into this (though bands, sports teams, etc. end up having the same problems frequently).
In my current group, we had a player who was just such a total goon that no one enjoyed games that he attended. People tried working with him, but finally we all got together and discussed the problem and ended up voting to disinvite him from the game. "He's making the game less fun" is more than enough justification.
In this case it's harder - is one person really the problem? Or is it both of them, but they're fine if the other isn't there? If they are both a joy to game with except when the other player's there, it's hard to decide which one to punt, but you can just leave it up to them. "Look, we like gaming with both of you, but it's unacceptable and fun-killing when y'all fight. Whoever starts it next time will need to leave." You can try giving people "time outs" short of punting them from the group - "You have to leave this session now because you're fighting." See if that shapes them up. I don't know how much you have invested in these people and how much work is justified to save the group vs. ditching one or more of the members out of hand. It's easy to be an Internet Tough Guy and say "throw them out, then ostracize them from your life!" because it's easy to say that when it's not you in that place. Don't jump to ejection before bothering to talk with friends, but also don't be afraid to pull the trigger once it's clear that's the only thing that will make the game fun again.