The big difference is AEL and NWLI are life insurers, where MKL and WTM are P&C insurers.
The stock market has been continually worried about the life insurers since the financial crisis due to their long time period of liabilities and corresponding investments, whereas the P&C insurer valuation has rebounded nicely as it is a simpler business with shorter term funding requirements and the ability to adjust premiums yearly as conditions change.
All lifeco's from the the big MET, PRU, MFC are valued cheaply, so it is not just a small company thing, but an industry concern. If rates stay low for 20 years like they have in Japan, there could be some serious issues for some of the life companies.
It's not the company that's an issue. it's the market and the China factor. I think at this price and value, it is hard to go wrong, but I would keep it a fairly small part of your portfolio as part of normal risk management.
What's the issue with KCLI? Were at $4. Announced a buyout of small shareholders and stock jumped to $47. Stock got over $50 as buyout approached (buyout was for $52.50). Buyout ended and stock moved to OTC Market, so has fallen back past $44 to $37.
Book value is around $70 and they have a good dividend.
Could be a good buy - probably temporary pressures of selling after the buyback and over market weakness causing problems.
Personally, I think NWLI is a better run company and it does use more conservative accounting, but KCLI is fine too.