Ollipop, thank you for your practical approach to thinking about things in this case. I happen to agree with several of the things you said in your last post.
For what its worth, here is what I am thinking:
No boat, paddleboat, pedal boat or otherwise.
No pre arranged meeting. There would likely have been prior contact between the girls and this individual via internet, social media.
The fact that the direction that the girls were heading may or may not make sense in terms of them heading towards the lake is irrelevant in my mind. Children on bikes typically ride one direction down a street or a well known route, and then turn around and ride the other way. Sometimes they even make small circles right in front of their house or on their street. This would agree with what WC said about having only to yell for the girls a few times and they would appear. At this point I am thinking that the girls were never at the lake either. I am now thinking the bikes were ditched, not staged after the abduction.
I think a stranger would be bold enough to snatch two precious girls off the street, even if they were in close proximity to their homes. The perps may have noticed they were not under direct supervision, even with little time to observe them and assess the situation.
The most common thread I have found among various abduction attempts is the tendency of the perp to stay in the vehicle even after initial contact, and then quickly leap out and grab the children. The perp will be outside of the vehicle it seems when using a more elaborate ruse or lure, but will have a second person waiting to whisk them away from the scene at the right moment. This minimizes the risk significantly.
I think there are two suspects. I believe they are younger men, late 20's or 30's.
Perps stop to get fuel in Evansdale. They are not local, but are enroute to somewhere else.
Girls riding bikes.
Perps spot girls.
Passenger perp makes contact with the girls from window of vehicle
Passenger perp either lures or forces the girls into the vehicle.
Bikes go into vehicle
Bikes and purse get dumped in a place that looks fairly secluded.
Perps get back on the freeway and continue on their way.
Total time required for their effort probably no more than 45 minutes, likely closer to 30 minutes.