Capital gain

No, your father need not to pay Capital gain tax if he invests the capital gains in another house property.

No, it need not to be registered in the name of your father alone.

But why can't you take one property fully in the name of your father and another house should be purchased by both of you brothers to avoid legal consequences.

There is no need to pay the tax on Capital gains if, he has invested in another residential property,

In breif, According to section 54 of Income Tax Act,1961, The transferor should have to purchase a new Residential house within a period of 1 year before transfer (or) two years after the date of transfer.if he palns to construct a house rather than purchasing, he has to construct a house within 3 years from the date of transfer

Amount of exemption from tax: Amount invested in new house property (or) Capital gains whichever is Lower.

Also you can claim Interest on borrowed capital u/s 24b to the extent of the share in house property.

deduction u/s 80C can also be taken towards the principal component  repayment towards home loan.

Exemption U/S 54 and 54 F of the Income Tax Act would be allowable for only one residential house.If the assessee purchase more than one residential house then the choice would be with the assessee to avail the exemption in respect of either of the houses provided the other conditions are fulfilled.

see in simple if your father invest for purchase of any property whose cost is more than 20lakh then  tax ll nt be leavy as you can claim sec 54. bt rember exemption as per various case laws decision is available only for 1 flat not both. bt still as they purchase price of each property is more than 20lkh so no cap gain in netting

Deepak What I am understanding from your question is that your father has one house with 18 year old costing Rs 1.5 lac. So that house must be purchased in FY 1998-1999 when index cost was 351 accordingly your today's cost will come to 4,61,965/-. SO your capital gain will be 20,00,000-4,61,965=15,38,035/-. 

So in order to get exemption from 54 your father need to invest Rs 15,38,035 in other house. Now your father is investing in two property with 50% share in each property with the investment of Rs 10 lac in each house. Now understand this as said by other professional colleague you will get exemption for one house only. So your father will get only 10lac exemption. On rest 5,38,035 your father have to pay capital gain tax.

Tax saving Tips

If you don't want to pay capital gain tax then you have two option. First your let your father invest in one house property with 100% share in property by this way he will invest 100% of capital gain in new assets or second option is that your father can buy 5,40,000 rupees bond as specified in 54EC.