A:AnswerAs long as your T3 has the canon EF mounting it should fit. You can probably do a google search to verify if the EF and EF-S lenses fit the T3.
A:AnswerYes the Canon 77D CAN take EF and EF-S lenses because it is not a full frame sensor, which these are. A full frame sensor DSLR can not accept EF-S lenses, which doesn't apply to the 77D.
A:AnswerYep. The 50mm is an EF lens that works with Canon crop and full-frame bodies. The 10-18mm is an EF-S lens primarily for crop-frame bodies like the 80D.