Can one make kiddush and eat in the sukah early on first,and second night of sukot if one are having elderly over?
This is fine for the second night of Sukkos.
For the first night, you have to be careful to make Kiddush and eat in the Sukkah only after nightfall.
For the first day of Sukkos, the Rema (639:3) rules that one must not eat before nightfall, as interpreted by the Magen Avraham (11) and Mishnah Berurah (25).
Accepting the second day of Yom Tov early is the subject of a dispute among authorities, as mentioned in siman 489 (the Taz is stringent, and the Kesav Sofer and Chok Yaakov are lenient). The issue is whether accepting the second day early is a pegam (flaw) in the holiness of the first day.
The Minchas Yitzchak (1:41-42) thus writes that for somebody who is sick or elderly one can be lenient. See also Rivevos Efraim (8:459) who is lenient, but does not present any sources.
Some, however, argue that those who dispute the ruling of the Taz only do so after it is dark, and not before it is dark (see Maros Yesharim 7). Where possible, one should refrain from accepting Yom Tov Sheini early – but for elderly people and a need, it is permitted.