It is better to fly to Varanasi kindly check the availability of flights. You need three days to spend in Varanasi. Here are some offbeat places nandeshwar ghat, Lolark gund, thulasi mandir and Durga temple. Stop by Chinese and Korean temple. You could plan a day travel to Khajuraho or Lucknow or Patna. Nalanda Chitrakoot and Satna are some nearby places to explore.
From Varanasi Ayodhya is 5 hours away. There are daily buses to this place. There are lots to explore in Ayodhya and you might plan for 2 days stay excluding day of arrival. To explore here are some offbeat spots- Ram ki paidi, Naya ghat, Mani Parvet temple and Tulsi Udyan.
From Ayodhya Allahabad is 4 hours away. Here are some offbeat spots of Allahabad - Alopi Devi mandir, Mankameshwar temple, Minto park, planaterium, and Allahabad library. You can plan for three full days to spend, explore and taste some best food.
In Varanasi you can explore
Kashi Vishvnath Temple,
Ramnagar Fort
Manikarnika Ghat
Ganga Arti
Sarnath
BHU
Sankat Mochan Temple
In Ayodhya
Kanak Bhavan
Saryu Ghat
Hanuman garhi
In Prayagraj
Sangham
Anand Bhawan
Allahabad Fort