Hello and welcome to the site.
Firstly,I don't see anything suspicious about the behaviour of your puppies,certainly nothing to indicate that you need to have them checked out.
Scanning at a young age is inconclusive,if there is no syrinx at the time of scanning,that's fine,but it would need to be repeated, as SM is a progressive condition.
Your puppies' mother has had an excellent scan,judging by the addition of the letter "a" at the end of the grading,she is over 5 and has a normal central canal.
Under the informal guidelines,any over 5 cavalier who was SM free could be mated to an affected dog and this is still true under the new guidelines,although the criteria have changed slightly.
I take it,an unscanned stud dog was used at the time of mating and has subsequently tested as an SM2.The lack of a letter at the end suggests the scan was graded informally and gives no indication of the age of the dog at the time of the scan.How old was he? If he was over three,and affected with a small syrinx,showing no symptoms,then the mating was within the new guidelines and would have been ok under the old guidelines.If he was under three at the time of scan, an SM2 would imply that he should not have been bred from under new guidelines.
I doubt the dog would have been symptomatic and allowed at stud and used by someone who had gone to the trouble of scanning a bitch.
Scanning is a very blunt tool,your puppies may have inherited a resistance to SM from their dam,there's no way to know.
A scan will tell you the status of the parents but cannot predict with any great accuracy,what the status of the offspring will be,but it allows a breeder to avoid mating two affected parents,thereby increasing the chance of healthy offspring.
It's still a genetic lottery,no guarantees,but at least research indicates that an over 5 clear will increase the chances of better scanning offspring.What you could do,is have both offspring scanned,maybe at two and see how they're doing,under a low cost scheme.
In the meanwhile,try not to worry about the babies,enjoy them,have fun and hopefully,they will remain well and live a long and happy life.
Sharing my sofa with Holly, Ivy,Lilly and Hazy.. and never forgetting our beautiful Daisy who reached the bridge too soon.