Is what the questioner did—marrying with the intention of becoming lawful for her first husband, then seeking divorce from the second, then returning to her first husband through an 'urfi marriage—considered forbidden? And is it permissible for her to live with her first husband under this 'urfi marriage due to her need for money and lack of shelter?

There is no objection to you returning to your first husband if your second husband divorces you and your waiting period ('iddah) ends. It should be noted that your request for divorce without a legitimate Shar'i reason necessitates your repentance. Your customary (urfi) marriage is valid if it fulfills the conditions of a marriage contract and was not intended to avoid documentation. As for circumventing regulations to receive the pension of the deceased woman, if it is a conditional grant, it is not permissible, based on the Prophet's (peace be upon him) saying: "Do not commit what the Jews committed, for they made lawful the prohibitions of Allah by the flimsiest of pretexts." And whoever fears Allah, He will make a way out for him and provide for him from where he does not expect, for Allah Almighty says: "And whoever fears Allah - He will make for him a way out And will provide for him from where he does not expect." The government pension, if it is among the entitlements of the deceased, is included in the inheritance and distributed among the heirs.