The multiple choice says both "אין לי יותר משניים., אין לי יותר משתיים" are correct. Why is this? Shouldn't it be only the feminine? Or do you gender it by implied object even though the object isn't mentioned?
Yes it's depends on the object you speak about even if it isn't mentioned here.
always you have a sentence without a clear gender,you must write it always in femenine form of the number.I read in tips and notes.
Unlike most words in hebrew when a number ends with ה it is referring to male and not female
Why do you need a מ in front of ths שתיים?
the מ usually means from, but in this case it probably translates as than
I used אין לי יותר משמיים and got the response:
אין לי יותר משניים.
Another correct solution:אין לי יותר משתיים.
שמיים = heavens / sky
When do you use שתיים instead of שניה?
They are two different words:
l שתיים - two
l שניה - second (as in first, second...)
What is confusing? If you need explaining, you need to provide more information than "confusing".
A number on its one is feminine, so it must be משתיים
Obviously, there was a masculine object in mind, when the sentence was written.
EDIT: upon second look, the sentence does have שתיים, so I am not sure what your comment meant.