The MOSFETs should be capable of carrying up to 200 A of current. Voltage is not that important it can stay low.
Use a distributor search engine or something like parts.io to find parts with the specifications you want.
MOSFETs in parallel each having a lower current capability
Yes this is possible. As more current goes through a MOSFET it heats up. As it heats up, the resistance goes up. Effectively limiting the amount of current that can go through it. This is called having a "positive temperature coefficient."
What will be the amount of heat produced from these MOSFETs if 200A is passed
Ohm's Law. P = I * R^2
Is there any issue of reliability
Good question for the manufacturer.