We are seeking divorce. Can husband ask for residence in wife's house?

Firstly, with respect to right of residence, under the Hindu Laws, the right of residence is only recognized for the wives. There is no such provision which gives right of residence to the husband. So you legally cant claim right of residence in the house which is gifted by your wife's brother. 

However, if you made any alterations in the last 25 years then you are entitled to that when the assets are distributed at the time of divorce.

Furthermore, do not leave the house on your own. She will have to move to court to get a vacate order so as to force you to leave the house. Until then you can stay in the house.

Now coming to maintenance, as you are also on pension, the Court shall be lenient while deciding the quantum of maintenance as it varies from case to case and it is up to the Courts discretion, there is no fixed formula.

Deciding the amount of alimony / maintenance is the discretion of the Court.

The sum and period of alimony generally depends upon how long the marriage existed. Marriages that lasted more than 10 years are entitled to be granted a life long alimony. Age of the spouse is also taken into consideration while awarding alimony. 

Normally, a young recipient of alimony gets it for a smaller period of time if the court thinks that he or she will soon be able to become financially sound through prospective career excellence. Alimony is also in vogue in order to equalize the economic condition of both the spouses. The higher earning spouse is entitled to pay a heavy amount as alimony.

The spouse who is projected to be enjoying a prosperous career is liable to pay high alimony amount. If one of the spouses is suffering from poor health, the other is subjected to payment of high alimony to ensure proper medication and well being of the other spouse.