Can two antivirus softwares work on one android phone?

Having one such app installed will not interfere with another. The biggest risk on a PC is that one AV app identifies the other one as malware, but the architecture of Windows is a bit of a mess anyway so it's easier for apps to interfere with each other on that platform.

These things can only detect malware types that the developer knows about and has created a signature for. So a new type of malware will at first not show up on any of them. Of course you have to be very unlucky to find yourself in that situation.

The vast majority of questions we get here from people worried that they have a malware infection actually have nothing of the sort. People tend to latch onto malware as the first explanation for any unexpected behaviour, when in practice it's one of the least likely. So if 2 scans have found nothing the most likely explanation is that there is nothing to find. But please feel free to describe your problem and we can see whether anyone has any ideas.

There are no true viruses for android (virus = malware that can propagate itself). Android malware is generally hidden inside an app that the user installs (what's called a "trojan", though following Homer's poem it really should be called a "greek" ). If you are sensible about what you install and where from it's actually unlikely that you'll ever encounter malware. If on the other hand you install apps from warez sites, uncurated download sites or pop-up ads then yes, that is risky behaviour. For most people the optimal number of "antivirus" apps to install is zero, but if you feel uneasy feel free to download one from a reputable company and use that (but check out the company first, not just app store reviews - a security app has all the permissions to own your phone, so it's very important that such an app is itself trustworthy).

 

If you are wanting peice of mind, you can always do a factory reset. That will revert your device and start you out fresh with no Spyware.

 

Your posting strongly indicates this is more a matter where you're so convinced that your phone has been compromised that you're using any excuse to 'prove' that it is. The issue being you can install one or a dozen more anti-malware/anti-virus utilities on your phone and until one of them does actually reveal there's a problem you won't be satisfied. Keep in mind there's no shortage of documented and well distributed number of studies that prove these utilities often create their own problems and that false positives are not out of the ordinary.
A lot of people read and hear all the fear mongering in the news media and instantly assume that every problem they have is because of a 'virus' or whatever but our smartphones are a very complicated mix of software and hardware (software consisting of literally millions of lines of code interacting with hardware make of millions of components). A bad line of code can be insignificant, or it could trigger a cascading number of failures that may or may not result in some kind of buggy behavior. So yeah, your phone could be 'infected' with something but it's also just as likely your phone isn't the problem. Odds are greater that one of your online accounts has been compromised (a user account matter that is only indirectly tied to your phone, or in other words it makes no difference at all about what phone you use, you need to regain control of your account). If this person was some kind of malicious black-hat hacker, stop focusing so much on what you see in the movies and TV shows. Here in the real world, really effective, potent spyware isn't going to be easily detectable, they're by design crafted to be invisible and transparent. Those apps you're installing from the Play Store are in the consumer marketing realm, when you install them and scan your phone to do the magic they claim keep in mind you've installed a utility that only has user-level permissions and as such can only do their 'magic' on a limited basis. A root-level exploit is immune to these consumer apps.

Curious as to why you apparently don't have a lock screen enabled on your phone. That's typically a 'must do' in today's world, especially when you leave your phone unattended.

 

The answer is that I've no idea how good those things are at detecting spyware, but I wouldn't bet my banking password on it.

I actually doubt that any spyware would be installed from the Google Play Store as that would make it too easy for you to spot (unless it's able to edit itself out from the list of apps you have downloaded from Google, which I'm doubtful of). But of course if you left someone with the device long enough they could download and install something from elsewhere.

Your phone only has a firewall if you added one. If someone knows the url of a spyware vendor - or somewhere they keep their own copy - then if you give them access for long enough they could install it and set it up. I'm not saying that is what happened, just that if you give your unlocked phone to a bad actor and leave them to it you have no security, as any protection you might have they could turn off and then turn on again when they were done so that you couldn't tell. The first rule is that you just don't give other people access to your phone - not just unauthorised access, unless you really trust them you don't give them access full stop.

What can you do? Well as Danny said, unless you left them alone with your phone, a computer, a USB cable and plenty of time they won't have rooted it(*), so a factory reset will clear everything - of course it will also erase everything on your phone, so you want to be sure you have a backup of your photos, messages etc first. If you are seriously concerned about spyware you'll change your passwords afterwards. And if you haven't enabled 2 factor authentication on your Google account, do so: if someone has access to your Google account then for many purposes they don't even need to put anything on your phone. Note: we occasionally get people who don't know their own Google login and password: if you are one of those don't reset the phone until you've worked them out, as you'll need them to get back in.

Not trying to scare you there, I've no idea whether you have spyware or not, just saying that if you have there are a number of steps you need to take to get rid of it and protect yourself against any leakage that might have occurred already.

(*) If your phone is rooted then they can put spyware in the system, where a factory reset won't get rid of it. But unless you have a really old phone you will need a computer to root it, if it's even possible in the first place.