TL;DR - I don't know how to calculate that as CR, but in all honesty, you shouldn't try. Focus more on how much it changes the action economy. When the players are outnumbered, or rather when the enemy team can make more actions in a round than the players, the players are at least threatened, if not in outright danger.
Long Answer: The big weakness of single "big bad" type enemies is that while they can do one or two really big things in a round, the party can do 5-8 small-to-medium things (or even more as players level and get more magical trinkets), and on the balance, more smaller actions is almost always better than fewer more individually powerful actions. Obviously if the big bad can one-shot PCs with a reliable attack, that is different, or if the players can't overcome some kind of DR, then all the attacks in the world wont help, but in general, the side with more actions will win.
So both of those abilities affect action economy in favor of the baddies. This isn't a problem, necessarily, but be mindful of how their use is impacting the battle. Dont use the abilty to summon skeletons till the players are outnumbered 3:1, even if they are "easy" targets for the players. Don't drop a debilitating AOE if the players are struggling to deal with the present threats.
If you are looking to use a CR5 monster as a mini-boss, and you are buffing this encounter, then your party is probably what, level 6-7-ish? If so, make sure the skeletons are strong enough to not get one-shot by a regular attack, and give some of them ranged weapons or some other means of controlling the battlefield, and give the wraith the ability to summon the skeletons to the squares they desire, so you can kind of "set" the battlefield in a way that makes it challenging and surprising, but fair. Save the AOE cloud as a tool to balance the scales if, after the skeletons, the PCs are still having a field day with the encounter. Something that blinds can be a really powerful effect, and if a lot of the players fail the save, you could have a quick turnabout. While the players still get to have their actions, they have their economy reduced still because fewer of their actions will actually accomplish anything.
In my opinion both of those are solid abilities to buff up an under-powered encounter, because they can present real danger, but you still have pretty good control over the circumstances under which the players will face the threats. Dont get too hung up on the numbers of CR except possibly as a guideline for not throwing the aformetioned unstoppable big-bad at a party. But you would be surprised just how unreliable CR can be as a gauge. A party of level 3 heroes with no/limited magical weapons versus a CR3 monster with DR can be very challenging, especially if that monster has a couple CR1 friends. Something that ambushes and paralyzes reliably paired with...just about anything, is dangerous. On the flip side, individual big bruiser monsters that can do ungodly damage in a single hit can be surprising pushovers because the players just focus on not getting hit and chipping away. And CR wont tell you any of that.
If you are looking for solid, well-explained DM advice, check out Matthew Colville's Running the Game series on YouTube. He explains this and other ideas even better than I do. The concept of action economy is a well-explored, if not commonly discussed, concept in DMing, and I think its one of the easiest things to give new DMs for their encounters but it seems like nobody ever offers this as advice.