The fact that there appear to have been two people aboard MH 370 with stolen passports would not necessarily mean foul play. They could, for example, have been used by people trying to immigrate illegally, who just happened to be unlucky enough to board a doomed flight.
If they were travelling together, then it is not unreasonable to presume they would have bought the tickets together or checked in together, which would account for them having ticket purchase dates and sequence numbers one after the other.
Two things make the connection more sinister:
First, their intended travel route. They would have transited in China, with final destinations in the EU. It is hard to see how they could have entered Beijing undetected, nor slipped out of transit at Beijing. More importantly, it is very hard to see how they could have made it into the EU on passports that were stolen so long ago and that would almost certainly have been picked up at Amsterdam (assuming, of course, that they would also have been able to evade detection when leaving Beijing).
Neither endpoint of their journeys seemed like a viable option.
Secondly, the fact that they booked different EU endpoints looks like an attempt to make their one-way itineraries less suspicious, suggesting the two were not travelling together. That may be explicable if they were trying to smuggle themselves into the EU, assuming they thought they could clear Amsterdam. But it seems much more likely that it was an attempt to conceal the last-minute, one-way, cash tickets. An attempt that, unfortunately, worked.