No, it is not from -아/어서. -아/어서 only applies a verb or adjective, not a noun like 혼자. In this case, 서 is a special particle that attaches to a subject showing number. It indicates the number in relation to the action. For example, - 혼자서 그걸 다 먹었어? Did you eat all that by yourself? - 이 작업은 두 사람이서 [or 둘이서] 해아만 한다. It takes two people to work on this task. (둘 means two, and 이 is added if the noun/number ends in a consonant, as in 셋이서 = in/by three) - 고등학교 동창생 넷이서 모였다 = Four high school classmates got together. 혼자서도 has another particle, 도, appended to 서 to add the sense of "even". So it means "even alone" or "even by yourself". So, - 혼자서도 되겠어요? = Could you manage even by yourself? - 혼자서는 못해요. = One person cannot do it. (는 adds emphasis, like "just one", especially in a negative phrase) - 둘이서 이 큰일을 할 수 있을까? = Can just two people handle this big task? 서 can be hard to master as it appears in many different constructs. It can be a contracted form of the particle 에서 (at, in, from), the verb ending -아/어서 (because) with 아/어 merged into another syllable , or a particle in its own right as in your example.

It means "even" or "but..still" So you're asking their opinion about doing it alone. Their feeling whether or not it is possible or if they are capable. That is the function of "겠" here. 혼자서도 되겠어요? 혼자 (alone) 서도 (even if/even though, etc.) 되겠어요 (is it okay)