Yes, I would put them together now. Pigs need a flight distance to settle who's boss, and don't have that in a trailer, and arriving with cuts up side and blood will not look good.
Under the Welfare of Animals Transport Order 2006, which implements EU 1/2005 it is illegal to transport:
• Pigs of different sizes and ages together, unless they are accustomed to each other
• Pigs hostile to each other together