> ... og mun sem vert er Þorleiki mest mein að þeim.

> ... and (it) will (be) when (sem, z5) most hurt is
> deserving (verðr, Z2) to Þorleikr as regards to (at,
> Z.iv.4) them (ie when his support of them will rightly
> cause Þorleikr the greatest hurt, cf also meinn, adj, Z1).

I don't think that this <sem> is 'when'; it seems to me to
be part of a phrase <sem vert er> 'as is right', parallel to
<þess væri vert> 'it would be right' in CV s.v. <verðr>,
making the clause 'and [it] will [be], as is right, to Þ.
[the] greatest hurt from them'. (<At> seems to me to be
A.IV.8 in Z.)

Reading it again, I agree with you.

> Eigi treystust menn að raska kosti þeirra fyrir Þorleiki.

> Persons (men) dared not to disturb their (Kotkell´s
> family´s) situation (ie drive them from their farm, kostr,
> Z5) for (because of, fyrir, Z11) Þorleikr.

My reading is closer to Grace's: I take <raska kosti þeirra>
'disturb their state/condition' to refer to any action that
would inconvenience or annoy them.

To support my translation, I refer to Laxdæla Saga, Mál og Menning (RIP L), 1993 student´s edition which provides this explanation of the expression: „raska kosti: (hér) flæma burt af jörðinni.“ Which I translate as „(drive away from the farm/landholding“

 

 

It won't show up on Google, but you might be interested in a
project of mine to which I hope to return one of these days:

<http://my.stratos.net/~bmscott/Landnamabok_Place-Names.html>