I use the following house rules for both Twin Strike and Careful Strike :
Careful Strike :
add critical on 19-20 for this attack
Twin Strike :
Target : one or two creature, one attack *per target*
This mirror the new fighter at will dual strike where you must use both attacks against the same target, make twin strike a (very) good minion killer, still increase the chance to at least use the quarry damage, provided you have at least 2 adjacents opponents, but it prevents it from overshadowing careful strike in its own niche : increased chances of hits againts one target.
Careful Strike :
add critical on 19-20 for this attack
Twin Strike :
Target : one or two creature, one attack *per target*
This mirror the new fighter at will dual strike where you must use both attacks against the same target, make twin strike a (very) good minion killer, still increase the chance to at least use the quarry damage, provided you have at least 2 adjacents opponents, but it prevents it from overshadowing careful strike in its own niche : increased chances of hits againts one target.