I don't know about all of it, but a lot of the time I've seen that the combined meaning is usually "x meaning" AND "y meaning", sometimes combined to mean "x relation to y", either way with both meanings kept in tact.
For example:
Atsuko: From Japanese 温 (atsu) "warm", 篤 (atsu) "kind, cordial" or 敦 (atsu) "honest" combined with 子 (ko) "child".
Chinatsu: From Japanese 千 (chi) "thousand" and 夏 (natsu) "summer".
Hanako: From Japanese 花 (hana) "flower" and 子 (ko) "child".
So I would think that what name -ren is a part of will still have 'lotus' as part of its meaning.
Anyway,
Ren can be used on its own as a name if you like, you don't need to combine it with anything. (see:
http://en.wikipedia.org/wiki/Ren#Notable_people) And when it comes to
Maren and
Karen... I highly doubt anyone would assume the meaning of those names to be anything other than the traditional meanings as listed by this site, as those are most common (are
Maren and
Karen even used in Japan in Japanese meanings??)
My PNL = http://www.behindthename.com/pnl/37275
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