How to fix my dual monitors.?

I use an HP laptop (running Windows 10) with two external Acer 27" monitors + 1 Acer 21" monitor.

* Monitor 1 connects to the laptop's VGA video connector with a VGA cable.

* Monitor 2 connects to one of the laptop's USB ports using a Diamond DisplayLink adapter which connects to an HDMI port on the monitor.

* Monitor 3 connects to another of the laptop's USB ports using a different Diamond DisplayLink adapter which connects to an HDMI port on the third monitor.

These adapters are about $50 each.

This way, I have a choice of mirroring the monitors or using each monitor as an "extension" of the laptop's monitor. Been doing this for years. Works great!

You told us nothing about your computer or what you need the monitors to display (all displaying the same thing or all separate images).

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The reason you're having issues is because the computer can't see all the external monitors - it sees the HDMI splitter as the "monitor". Everything else past that (the actual monitors) does not matter to the computer.

You will need at least a dual monitor card.  Some have one port with a dual output cable or a dual port, which would have 2 ports and 2 single cables.  A splitter like you have is probably so you can switch between a monitor and a TV or something like that, that is the output to be shared not multiple screens like you want.

when you use a splitter the PC only thinks there is one monitor and the picture will the the same on all of them.

you need to connect the monitors to different ports.