That sounds interesting, i guess the hardest part is to survive long enough to get to soulmate level.
My characters die a lot in their first few levels due to mostly stupid mistakes.
Something good to inherit i think would be balls filled with strong monsters, so the next generation can start with powerful allies to avoid them perma dying in their first few levels. But that require the previous gen to have survived enough to be able to capture a strong monster with a high enough leveled ball, with perma death it's easier said than done.
About living weapons, are they that interesting ? i mean from reading about them after they level they gain an unavoidable "eat the weapon user own health point" horribly bad skill that sound rather nasty when you're in difficult fight.
Living weapons are (in E+ and derivatives) guaranteed to develop the "it sucks the blood of the wielder" enchantment at every level beyond 10. You can safely take them to level 10. In other words, you get ten choices for what enchantments you
want rather than a random set. Even a plain living weapon with no starting enhancements will be better than anything short of a perfect Godly artifact simply because you get useful stuff instead of "It maintains X" and random skill boosts.
The most universal option for leveling one is to add +4 to the enhancement bonus, which is always available. This ignores the normal +10 cap (make sure to get to +10 with scrolls and a smith
before you use this), and (if you weren't aware) works the same as in D&D, so you can end up with, say, a +30 weapon, meaning +30 to-hit and +30 damage on top of whatever else you choose.
You can add increased critical hit chance, piercing attack chance, enhance spells (for a mage's statstick)... and that's about all you want to use. The skill/attribute bonuses are shit (except for Speed, which is still not a good pick). Elemental damage is okay in Act 1 but falls off. Elemental resists are bad bad bad unless you're doing them on a statstick you aren't going to be attacking with (like a bow on a mage or a dagger on a gunfighter).
They shine even more if you spam sharp equip making crafts until you get ones with good innate enchantments. My Claymore has a pair of living claymores I crafted with [####] enhanced criticals and Invokes Regeneration [#####+]. Shit outshines basically anything you're ever going to get naturally. Even just going straight to +50 enhancement bonus will be better than pretty much anything, but adding crit is almost always good too.
Used to be that you could abuse scrolls of name and material kits to indefinitely avoid generating bloodsucking on levelup, but that's long since been changed.