Just want to know the below complex sentences are grammatically correct?

Just want to know the below complex sentences are grammatically correct? Thank you.

Although the concept relating to the financial crisis was complicated, the professional, who had been thoroughly trained, was able to explain it and its great impact on our economy.

2. A gang of terrorists, who ignored the consequences of being killed or jailed, set off bombs deliberately in crowd areas, causing serious injury or death to people in Paris.

3. People should make more friends and share their feelings in order to relieve stress, which can cause a lot of serious problems such as low self-esteem and self-harm.

4. Police have been trained to be more cautious about any signs of terror attacks, however, It is difficult for them to prevent attacks in some situations, include terrorists posing as refugees to enter Europe.