(1) It is unlawful to take interest based loan from a bank in which one has to pay interest. As it is unlawful to take interest in the same way it is also unlawful to give interest. But the amount which he received from the bank is debt and it is lawful.
(2) It is a sin and unlawful not to pay electricity bill i.e. doing electricity theft.
(3) Please, clarify what types of tax do you mean. Thus the amount of loan was halal. If he gives gift from it or he has any other income source and gives gift from it then it is lawful to accept such gift. Yes, a person whose most of the income is unlawful it is must to avoid taking his invitation or gift. If the said person is involved in unlawful activity, paying interest and electricity theft then and you avoid taking his gift to show undesirability then it shall be taqwa and precautionary act, which is appreciable, but as per the fatwa you can practice what is mentioned above.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband