I did this over 10 years ago, though the circumstances were slightly different.
Our property was valued at €320k at time of the agreement to buy his 50% share out. The prior joint mortgage had been held by my sibling and me for about 5 years before we agreed that his share would be bought out by me.
There was no need for a deposit. The bank gave me a mortgage for €320k and from that, the prior mortgage was paid off and I became solely responsible for the new mortgage when I became sole owner.
Talk to the bank, they’ll set out their expectations.