Both the Sunni and Shia branches of Islam have and support terrorists groups. Both branches have many divisions creating many sub-branches. Each layer or group “interprets” their religion differently. Some groups are peaceful, others are not.
Here are some of the Islamic backed terrorist groups. Not sure I have all of the terrorist groups classified under the correct branch of Islam? But it is the best I could find.
Sunni Terrorist groups.....................Shia Terrorist groups
Al-Qaeda.................................................Hezbollah
ISIS..........................................................Hamas
Taliban
Boko Haram
Al-Shabab
Muslim Brotherhood
Feel free to correct any mistakes I made, or add to this list any terrorist groups I may have missed.
I picked one on your list, pretty much at random.
Hezbollah. This is in terms of the size of the militaries on both sides in Syria.
http://www.washingtoninstitute.org/policy-analysis/view/who-are-the-foreign-fighters-in-syria
(Sunnis, e.g. ISIS)
On the side of the Sunni Arab rebels, a conservative estimate would place the number of foreigners at 5,000 individuals, while a more liberal estimate could be upward of 10,000. These totals are for the entire conflict, not necessarily how many are currently on the ground there. Many of them have been killed, arrested, or have since returned home.
(Shiites, e.g. Assad, Iranians, Hezbollah)
The large majority has come from Lebanon and Iraq, but there are also Iranians and others. The total number is at most 10,000. Lebanon's Hezbollah has sent between 3,000 and 5,000 fighters in total, but the number at any given time is lower since they serve on rotating monthly tours. There could be between 3,500 and 4,000 Iraqi Shia fighters, and credible sources speak of 1,000 to 1,500 members of the Islamic Revolutionary Guards Corps (IRGC) from Iran.