Help System read/write issues

[BlackoutFX]

Hello, I am new here, so sorry for any obvious mistakes a noob to forums and this website would make.

I am having a serious problem going on with mounting my /system partition as r/w... I recently removed a lot of system apps to free up space on this Cricket HTC Desire 625, and I pushed some other files onto /system partition as alternatives, such as a modified YouTube app that would work without Google Play Services.

I factory reset the phone via settings, and since then, I have lost access to /system partition, and I am struggling to regain r/w permissions. I still have root (SuperSU) and I even have TWRP and an unlocked bootloader. However, I cannot find a ROM to install to see if that may fix it, as there are no ROMs available online for this device. My main problems are...

• Apps around 20 megabytes in size or above will automatically crash if installed as a regular app (/data/app/*app folder*/*app itself*
• Before I knew that it was stuck on R/O only, any time I would attempt to move an apk to /system/priv-app to make it a system app so that it would work properly, for a split second my file browser would tell me that it failed, and the device would reboot.
• I attempted to mount R/W through terminal on device itself, and I would get "invalid argument" when trying to remount /system as r/w, even when using ADB I still get it. (I used the mount -o remount,rw /system command, I also used adb remount on both recovery and normal boot)
• Only really small apps work. (For example, Root Explorer)
  
• I cannot even mount /system on twrp as r/w.
• I cannot flash any zip files from twrp that would modify /system partition, I don't have BusyBox installed.
• When I modify /system in TWRP it boots the device and exits TWRP
• I attempted to push apk files to /system/priv-app via ADB, however, the files would come through halfway and my device would reboot

Can someone PLEASE, either link me a stock ROM for Cricket HTC Desire 625, or help me remount as r/w? I cannot even backup /system partition in TWRP.

Thanks in advanced.