I have searched but didn't get any exact hadiths related to it that more than one prayer can be offer in one ablution or we have to perform a separate ablution for every prayer.
Yes, praying with the same wudhu is valid. Although, it is Sunnah to perform ablution for every prayer as the Prophet (ﷺ) used to do so.
Narrated 'Amr bin 'Amir:
Anas said, "The Prophet (ﷺ) used to perform ablution for every prayer." I asked Anas, "What did you used to do?' Anas replied, "We used to pray with the same ablution until we break it with Hadath."
No it is not necessary to perform a separate ablution before every prayer.But if you do separate ablution for every prayer it is more good.
if you already have wudu then it's not necessary to make another wudu, but it is recommended. As far as you don't make any thing that destroys your wudu. you can offer separate salah with single wudu.
Ablution is sunnah we are blessed with this before every prayer. But it's not necessary to perform ablution before every prayer if you already have it. But it's good to perform ablution before every prayer if you are on road and any other place where water is not available you can pray with your last performed wadu if it is still you have. And the other side is that if you are at home and a place where you can easily perform ablution than do it.