1. You and your mother can avail the exemption equivalent to the LTCG arised irrespective of your share of investment in new property. Investment in joint property is eligible for exemption.
2. No implication. The clause of co-owners and the percentage of investment should be very specific.
3. Get the ITR filed by CA. He wil ask for the purchase deed, sale deed, bank statements, copy of purchase deed of new property and valuation report if any.