Jointly assessed, one PAYE one newly self-employed, tax registration question

I asked Revenue via the online enquries in MyAccount about how my wife should register as a sole trader for income tax (their website seems to suggest she can't via online as we are jointly assessed and instead must use a TR1).

Interestingly, Revenue came back with this which has me very confused now...

"In cases, where customers have chosen to be jointly assessed for Income tax with their spouse, the Income Tax registration must be set up under the tax registration number of the assessable spouse.

According to Revenue records you and your spouse are jointly assessed, with you being the assessable spouse, therefore the Income Tax will have to be registered under your name.

Income arising from all sources must be returned under your PPSN.

If you have issues registering for Income Tax on Myaccount, a TR1 form can be completed and submitted to register for Income Tax."

So are we to complete a TR1 in my name as if it's my business even though the business will be operated by my wife?

I can understand the confusion. Either two options - make your wife the assessable person or go for single assessment. The assessable person is the spouse that is assessed for tax where both spouses are asssessed together. This is called joint assessment. If you wife is the assessable person it will be her tax number that the business will be taxed under.

Do you know if there's an advantage to one over the other? I'm the assessable spouse as my income will be much larger than my wives. Her sole trader income will be low but over the €5K limit so she needs to set up as sole trader. (Last year I was able to just add her income to my end of year return as it was below €5K)

"...or go for single assessment."

A bad, bad idea.

Just wondering is another option to put everything in my name even though I'm not running the business and invoices will be in her name? (going on the Revenue guidance?).

I did note on the TR1 form there is a section on the form that asks for info on your spouse (name and PPSN) so not sure if that is how it'd all get sorted out in the end using my wife's name in all other sections.