Cellmate1234
Wraiem
Look into calisthenic progressions. Convict Conditioning might be a good place to start. The idea is to make the movement done in a different way. Can't do a pushup? Try them against the wall first. Then over time, your hands move closer to the ground. I wouldn't worry too much about situps, however.
Calisthenic...? All I know is that's old people stuff x) and I looked up convict conditioning before and all they had was pictures with no words ._.
Simply put, calisthenics = body weight + gravity - equipment
Find video of the progressions on YouTube.
Here is a playlist for the Pushup progressions.