Dear Querist,
Basing on your feedback, I have to advise you as follows:
1)Pl. go through all relevant provisions of your Partnership Deed including that of dissolution of firm, since you have proposed that all existing partners will opt pot of the firm and the business will be handed over to two new promoters.
2)In case, you want the Firm name and business to continue as usual in the hands of new promoters (partners), you have to admit these new promoters in the existing firm as per provision of Admission of new partners stated in the Partnership Deed of your Firm and thereafter all three existing Partners can retire from the firm alongwith their share of capital as per procedure.
3) In case, your Partnership Deed is silent on any such matters, provisions of Indian Partnership Act shall prevail.
Hope this serves your purpose.