Need to borrow 100K, hope to repay within a year, need advice

Hi, 1st time posting..
Myself and my partner need some financial advice on
buying a house/mortgage.
I have been offered a house by my aunt but she wants
the money asap.The house costs €100k so i will need to
take out a mortgage for 100K.
My partner has her own house and is putting it up for
sale soon, i'd expect the sale to take a few months in
the current climate and we expect to make 100K profit on
her house. The plan is that we use the 100K profit (or most of it) to pay off
my mortgage in a few months time.
Because of our circumstances i was thinking she should get the mortgage for say,
a 35yr period so our repayments would be quite little until we pay off our mortgage.
My question is: are we entitled to do this? Is there any penalty from the banks? Is
there anything else we should consider?
(We CAN'T wait for the sale of my partners house to buy this one)
Any advice appreciated.

As long as you take out a variable rate mortgage you shouldn't be penalised for paying it off early or making a lump sum payment.

and it would be advisable to go for an interest only option if possible.

Is there 100K equity in your girlfriends house? Does she qualify for an additional 100K? Is she in a position to make the additional repayments?

To get the best rate available I wouldn't necessarily tell the lender of your plan to pay it off within one year.

She bought the house 2 years ago.. She used 50K of savings and hopes to make 50K on the price she paid.. It's very doubtful she would qualify for an additional 100K, why would this be of benefit?

Go for an interest only mortgage. There are many brokers who can advise you on the best deals out there, but sounds like that it the kind of thing that would best suit your situation. The repayments are low enough. Just make sure there is no penalty clause for paying it off early.