Should I worry for the apps from untrusted enterprise developer in IOS?

Whether or not you should worry is highly individual and cannot really be answered in general.

First you write that you "have to" install these apps. Why would you "have to" do this?

If this is mandated by your employer, you could try arguing that you need a work device issued by that employer.

If this is mandated by your government, there's probably not much choice in the matter and you would need to take your own precautions regarding your personal data.

Second, it is impossible for us to know how important it is for you to keep your personal data safe and private. Do you only have mundane text messages from your employer and a few standard photographs of scenic landscapes - or do you store highly sensitive data such as data about your health or even evidence gathered for an upcoming lawsuit against said company?

You would need to do a risk assessment and figure out what kind of risk you can tolerate.

Essentially, enterprise apps are supposed to "play by the rules". The enterprise developer is bound by a contract with Apple that restricts them from various nefarious activity - however, this particular company might be willing to breach contract. It is hard to know without knowing which company, we're talking about.

Enterprise apps are run in the same sandbox as ordinary App Store apps. The main difference is that these apps are not subject to the standard App Store Review by Apple before being allowed to be installed on devices. This means that an enterprise developer could be exploiting bugs in the operating system in order to break out of the sandbox.

It's not something that's normal for enterprise apps, and not something you would expect from a big corporate employer in a modern country... however it is a risk.

You should not put much extra meaning into the fact that it states "Untrusted Enterprise Developer" - it doesn't mean that this is some particularly bad or untrustworthy enterprise developer. It simply means that this is the first time you're installing apps from that particular enterprise developer, and that the device is not managed (MDM) by that company.