Why were they nice to Beth?

To gain her trust I guess.. Probably they figured out she wasnt as dumb as the other two chicks, so they had to take precaution

nostalgic value.. and all that

They sized the group up. One is naive and nerdy(easy target), one drunken partygirl(also easy target) and she was the one who looked out for everyone which is why the trust needed to be gained in order

They tried to simply have her taken by the henchmen, she escaped. They took her home and called the henchman to come pick her up.

But it doesn't make sense entirely how the abductions take place, similar as in the first part. There was no need for the girls to party and sleep with the guys, elite hunting could have just abducted them at night using force.

It's a plot device. The film maker decided it would be more entertaining and less redundant to have the 3 women treated differently. For me, having them initially treat Beth well is a major hole in the plot.

Beth sold for $500K. She's very valuable and was treated as such.