Various options for joint registration/will/gift

My father aged 90 years, sold his house , of about 60 years. He is Keen to acquire a flat in Manesar costing almost same amount as received in the sale. We are three brothers and two sisters, youngest brother is a US citizen since 20 years. Since we all have our properties in India,we feel that our youngest brother in US must also have some property. My question is: 1. Should we get joint registration in the name of my father along with the youngest son. This will ensure that our youngest brother remains the co owner right from the start. If so , Is his presence required for registration of sale deed in tehsil office? How will the remaining portion be transferred in his name as and when the call comes. 2. In case the property is not registered jointly now, what are the pros and cons of gift vs will in his name. 3. We have given the advance money and sale deed is to be executed shortly. 4. Request clarify issues regarding capital gain tax ,if any, 5 Total money is being paid by my father which is equal to the payment received by him in the sale of his house.In case of joint registration, will it be taken that my father's share can not be total. An early reply is requested.