In quran it is mentioned that you cannot marry or have intercourse with your sister but can we touch them with lust without ejaculating, can we touch their awrah what is between navel and knee over their clothes?
It is haram to look at or touch a mahram (such as your sister) with lust. A Mahram by definition is someone with whom sexual intercourse is haram. A mahram can not be made lawful, even by means such as marriage which make other women lawful. And the precursors of sex (such as lustful touch) come under the same ruling as sex itself.
وقد اتفق الفقهاء على أن النظر إلى المرأة بشهوة حرام، سواء أكانت محرما أم أجنبية ... متى حرم النظر حرم المس بشهوة
The jurists are in agreement that it is haram for a man to look at a woman with lust , regardless of whether she be his mahram or a stranger ... and what is haram to look at is also haram to touch with lust
Consensus is evidence by itself. Further it is also evident by reasoning from the following texts:
والذين هم لفروجهم حافظون إلا على أزواجهم أو ما ملكت أيمانهم فإنهم غير ملومين فمن ابتغى وراء ذلك فأولئك هم العادون
And they who guard their private parts. Except from their wives or those their right hands possess, for indeed, they will not be blamed. But whoever seeks beyond that, then those are the transgressors.
This verse forbids obtaining sexual pleasure by means of any person other than your wife or concubine. Touching with lust causes ones private part to experience pleasure, and is contrary to 'guarding' it. Hence it comes under "whoever seeks beyond that" and is haram.
ولا تقربوا الزنا
Do not even go close to fornication
Touching with lust tempts one closer towards zina. Zina with a mahram is haram. Whatever invites one to Haram is itself Haram.
فالعينان زناهما النظر ، والأذنان زناهما الاستماع ، واللسان زناه الكلام ، واليد زناها البطش
The Zina of the eyes is looking, the Zina of the ears is listening, the Zina of the tongue is speaking, the Zina of the hands is touching
Looking and Touching are types of Zina. Hence they are haram and must be avoided. Zina with a mahram is more reprehensible than Zina with a non-mahram hence is more severely haram.
قل للمؤمنين يغضوا من أبصارهم
Tell the believing men to lower their gaze
This is a general and unconditional command to lower one's gaze i.e. to not look. By default it includes looking at mahrams with lust - as there is no evidence which excludes it. And when looking is haram then touching is worse than that, so it is also haram.
وفرقوا بينهم في المضاجع
When your children become ten years old ... arrange their beds (to sleep) separately.
This is to prevent any immoral act between the males and females. Touching with desire is more serious than sleeping together and hence is more deserving to be haram.
Abu Huraira reported Allah's Messenger (ﷺ) as saying.
Allah fixed the very portion of adultery which a man will indulge in. There would be no escape from it. The adultery of the eye is the lustful look and the adultery of the ears is listening to voluptuous (song or talk) and the adultery of the tongue is licentious speech and the adultery of the hand is the lustful grip (embrace) and the adultery of the feet is to walk (to the place) where he intends to commit adultery and the heart yearns and desires which he may or may not put into effect.
[Sahih Muslim 2658a]
As stated above, touching or grabbing someone with lust would be adultery of the hand. And we all know that adultery is haram (prohibited).
Hope that answers the question.