MB4 260b: Making an Eruv on Yom Tov (393:1-3); Safek Eruv (394:1)

An eruv chatzerot/shituf mavuot can't be made on Yom Tov that falls on Friday (it looks like הכנה/תיקון). If a person made an eruv on a Friday-Yom Tov does it work בדיעבד?

Making an eruv on a three-day Yom Tov for Shabbos with a תנאי (except Rosh Hashana).

Making an eruv chatzerot during Bein Hashmashot or after making early Shabbos.

If you don't know if the eruv food lasted for the entire duration of Bein Hashmashot.

Safek if it was placed there or not vs. Safek if it lasted for the entire Bein Hashmashot.