The success of your team depends on a united effort towards the common goal. As a leader, you cannot force your team members to like each other but you can create an environment that enables them to develop their relationships. Assign a project jointly to those who have difficulties with one another. Nothing big, but somehow challenging with a good chance to be accomplished. It will allow your people to get to know each other and develop some level of trust. Team building goes beyond a virtual or physical scavenger hunt, it is an ongoing agenda item of leadership.
You’re under pressure because you definitely started this important project too late. How