have bought but they have not reserved any seats as requested saying it is not possible.Will be travelling in 10 weeks time. Can I take tickets to the station of departure and ask for reserved seats in the meantime?
Yes, although you'll need to collect the tickets first and take them to the ticket office. It doesn't need to be the station of departure, any ticket office will be able to do so.
Although consider that whatever problem lead RailEasy to be unable to reserve may also effect the ticket office. Remember not all trains are capable of being reserved.
Source: Done so many time repeatedly, it's also mentioned on this national rail page: https://www.nationalrail.co.uk/times_fares/ticket_types/46581.aspx