せめて

"At least"; "if nothing else." When the full or ideal outcome is out of reach, the speaker scales down to a minimum and wishes for, asks for, or settles on that much.

Used in everyday speech and writing when settling for less than one hoped for. It often follows a concessive clause such as ～ても or ～でも that states what is impossible, and is commonly reinforced with だけでも, ぐらい or だけは. Unlike なるべく, which aims at the maximum possible, せめて sets a lower limit.

• なりともN1「なりとも」 attaches to nouns, typically minimum-quantity words like 「一度」 or 「少し」; it is fairly formal, sounds more weighty than 「でも」, and often appears with 「せめて」. After a question word it can also mean 'whatever / no matter', as in 「何なりとも」.
• ないまでもN1「ないまでも」 is a conjunctive form attached to a verb's ない-form and the like, and you must state the higher standard that isn't reached; it is formal and, besides setting a minimum, can assess an actual degree ('though not quite…, still…'). It often pairs with 「せめて」 in the same sentence.
• だけはN2「だけは」 must sit between two instances of the same verb (「言うだけは言う」) to mean doing at least this much or doing what one can, whatever the outcome. 「せめて」 is an adverb expressing a minimum wish or small consolation, so the two are not interchangeable.
• たりともN1「たりとも」 follows 「一」 + counter or 「何人」 and takes a negative or prohibition to mean 'not even a single…', sounding formal and stern. 「せめて」 means 'at least… would be good' and mostly goes with wishes or requests, so the two are not interchangeable.
• なるべくN3「なるべく」 means 'as much as possible', striving toward an upper limit; it directly modifies verbs and adjectives and can be followed by a negative. 「せめて」 falls back to a bare minimum, often pairs with 「だけでも」, and can describe facts already settled, so the two are not interchangeable.

「せめて」 is an adverb expressing the speaker's subjective wish for a bare minimum; 「ないまでも」 means 'even if not X, at least Y' and often pairs with 「せめて」, while 「なりとも」 attaches to nouns to mean 'even just a little', is more formal, and can also be used with 「せめて」. 「だけは」 limits the scope to 'at least this one thing', 「たりとも」 in 「一～たりとも」 + negative means 'not even one' (the opposite direction), and 「なるべく」 means 'as much as possible', expressing the degree of effort with no sense of settling for less.