Two of out of four party member are inconsistently participating due to their jobs. Up till now that was not a problem for us since we were playing self made adventures but now we start Wrath of the Righteous and are confronted with the problem of how to give these people experience.
I would like to know if there is a way (hopefully in the rules) that handles this problem or gives advice.
I played with a GM who would only give XP for people who showed up, and after a while it was a bad time as it became more and more difficult to create encounters that were challenging-yet-survivable for everyone. In a cooperative game, making some characters significantly less effective also punishes the rest of the group. So I really wouldn't advise that, even if it's suggested in the rules.
Your course of action here really depends on what you want to achieve. Ideally, the game is fun enough that everyone wants to show up every time, so that by itself is enough incentive for people to come when they can actually come. If you're dealing with some flaky folks, some form of "punishment" may be appropriate, but especially since you said the absences are due to work, I really wouldn't do that in this case. So I would give everyone the same share of XP (or, as some others have suggested, just level up the group at appropriate narrative/time intervals.)
I can see how, as Cyberspark says, that could feel like they're getting all the rewards with none of the risk, and that could feel unfair. But that needs to be talked out in your team. Again, I would argue that the real reward of showing up is that you get to play and participate in the story, and when you are all together again, you don't want to deal with some members of the party not being able to effectively participate. But if that's not enough, you can:
In this way, the characters of the players who show up will eventually be more fleshed out and have slightly more influence on the plot of the game, while no one is actually hampered by significant drawbacks the way they would be if some characters were lower level. And it's also not a punishment that you're explicitly doling out to people who really couldn't help the situation; just the natural progression of things.
By the way, you should also discuss, among other things, how deadly the adventures will be and how absences will be handled - in a party of four, if one or two characters are conveniently elsewhere for an adventure (one of the standard ways of handling this), the rest could find themselves unable to accomplish the task at hand. But if you include everyone and play the "missing" characters yourselves, you'll have to either A) risk death or other serious setbacks to a character while their player is away, which can be quite frustrating; or B) go through some amount of inconvenience as a GM to make sure there's no real risk to those characters. How much of a problem this is depends on how risky your game is to begin with, but it's definitely worth establishing in advance so no one is caught off guard.
We normally handwave XP distribution altogether and just level everyone up after a significant amount of time or achieving campaign goals. While writing down XP has a certain charme and old school vipe, we don't feel that the game really benefits by following the standard formula.
Nothing in the rules mentions variable group-sizes. But it depends on how willing to punish and reward those who can't always make it.
According to RAW I suppose you should be dividing gained experience only by the number of characters/players present.
Naturally this means that your frequent absentees are likely to fall behind in levels. You could always divide by four and grant experience regardless of them turning up, but then you risk those that do show up feeling like they could benefit just as much by not turning up, without risk to their characters.
This is more of a DM decision and social engineering than simply following the rules.
One thing that I've had some DMs do is forget about XP bookkeeping altogether, and just tell everyone when to level up based on what makes sense for the story. This seems to work just fine for keeping everyone at the same level. I'm away from my books right now, so I'm not sure if this is an official rules variant or not.
