Can I carry work laptop with B-2 visa?

This is not particularly uncommon, and there certainly isn't a rule against it. Many people visit the US on vacation and may find it necessary to send some work emails or check in with their office, and they do so without incident.

That said, as you've heard, if you do arise the officer's suspicions, you may be refereed to secondary for further examination into your travel plans to determine whether you should be admitted to the US. Approximately two percent of travelers are sent to secondary screening. As part of that, your personal belongings may be searched and you may be questioned about them if they lead to inconsistencies in your story. A classic example would be someone who says he is coming as a tourist for a week of sightseeing, but brings a month's worth of clothes and copies of his resume, academic certificates and diplomas, and letters of recommendation for a job. Another would be someone who says he doesn't know anyone in the US, but whose phone contains text messages about how he can't wait to see a significant other.

Such situations are evaluated on a case-by-case basis, and if you've gotten to that point, they're already suspicious of you for one reason or another, but I don't see that a work laptop would be the end of the world in and of itself. A work laptop shows stable employment elsewhere, which could help indicate an intent to return home. The important part is having a good clear premise for your trip and evidence of ties to your home that show you will return there as planned. Showing such ties may be more difficult with your wife living in the US, but evidence of your job back home could count in your favor.

In addition, CBP maintains that it has the right to search laptops and other electronic devices and the data on them at the border, including taking them for further inspection. Courts have generally gone along with that argument, citing CBP's authority to search all goods entering the country, even when there is no evidence to suspect you of wrongdoing. The linked article provides a guide from the Electronic Frontier Foundation with useful information. Such searches are rather infrequent indeed, but you should be aware they are a possibility and plan accordingly.

Questions about a dependent visa are off-topic here, but would likely be on-topic at expatriates.stackexhange.

Can I use the current B-1/B-2 visa?

Yes, as it is valid for the purpose of your trip and has not expired.

Would they question me for carrying a Work laptop and if so, can I answer them that I would like to check my office mails during my vacation?

No, they will not. They will not care if it is a work laptop, a personal laptop, a friend's laptop. If the laptop is on your person, for all practical purposes it is your laptop; and you are responsible for all content on it.

Also I may apply for dependent visa if I do not get the H-1B from here?

You already have a B1/B2 visa. Why do you want to apply for another one? Anyway, if you are asking can you have two valid visas for the US, the answer is yes, assuming there is justification for the same. However, from the State department we have this:

Applying for a new visa is not necessary if your visa has not expired and you have not exceeded the number of entries permitted on your visa. Multiple uses of a visa must be for the same purpose of travel allowable on the type of visa you have.

And finally:

Do I face any issues while applying dependent due to the number of visits?

No. Unless any of those vists were againsts the length and purpose of the visa under which is was undertaken.