Can i have malwarebytes same time with avast and does avast block ramsomwares?
Sure.Yes it does.
ok so do i need malwarebytes then?
It provides additional, multi level protection in depth.
Also install MCShield. It protects USB drives from spreading infections. When a USB is inserted it automatically scans for malware. I have been using it for a month now and loving it ;). MCShield is completely FREE
ok thanks 
Your welcome 8)
Unnecessary with Avast!
Not true, MCShield will scan automatically when usb is plugged in, Avast will only scan when accessed.
Take a look in the viruses and worms forum section and see all those that have been infected from USB malware not detected by avast and the malware removal team have used MCShield to clean the comp/USB device
Historicly the MBAM Team has verry good relations with Malware Removal Specialists on different fora, and they use their knowledge/feedback to target specific Malware families.
Greetz, Red.
About MCShield, most of us Evangelists are using/recommending it for a reason 
Greetz, Red.