Assuming the person the OP is speaking about wants a relationship and (nuclear) family (as stated, that would need to be in place, obviously), I am not 100% sure that every autistic person will find it easy to have these things. The simple and painful fact is that even many NTs struggle to have these things.
I do have a husband and children. Sometimes it's pretty hard (although I adore my children, they are my very heart). It is VERY hard, as an autistic person, to deal with loudness, constant dirt/disorganization everywhere...etc. Being in many ways touch-avoidant/needing personal space whereas my ASD son requires very hard pressure and grabs on tightly, shoves his face and chin hard into my face, etc. It can be very, very, very hard.
But for me it's been doable. I don't know about for the next person.
I feel my father was probably HFA (I mean he was practically an autism sterotype, in retrospect)...and he couldn't deal with any of it. He beat us all in reaction to what he found painful - our noise, my constant crying (everything bugged me, sensory stuff, and I cried), the disorganization, changes of plans as will constantly happen when kids are involved and necessary things come up, illnesses and on and on. Then he and my mother broke up, following 12 years of marriage. I was 8 at the time and between then and the age of 18 - so, 10 years - I saw my dad I think 6 times total. That was about the extent of "child" he was able to deal with, his stuff being put out of his carefully organized order, unpredictable emotions, unpredictable reactions and changes of plans/restructuring of his weekend and so on. I could see the whole business was physically terrorizing his sense of order and his sensory stuff, I mean he'd clutch his head. He'd be ready to melt down at any given moment.
My father did find happiness, but not in a family that had children in it...he DID have a life mate, though. They were together for I think 20 years before getting married (he knew he was dying and wanted to protect her interests once he was gone). But they lived a VERY regimented lifestyle. For instance, dinner was at 7. Always at 7. Never at 6:50. Never at 7:10. A change in scheduling would always all but guarantee a meltdown on my father's part. He couldn't handle changes. And they both refused to be interrupted during dinner. A call could come through and play on the answering machine that a family member had been run over by a car and was hospitalized and they WOULD NOT interrupt dinner, you just can't do that, finish first, then make the call. She was VERY patient with him, tiptoed around him. Could never raise her voice (loud noise hurt him, just as it hurts me). Could never act emotional, as he felt but didn't really "understand" emotions. Could never ask anything of him outside their accepted routine. And so on. But you know what? It worked for them. And FTR I do not believe she (the wife) is autistic. She fell in love with his brain and reorganized her entire life and way of doing things, for him.
It can happen, but it takes a ton of work - as I said, even for NTs it takes a ton of work. Go on any "relationships" forum anywhere and you'll see dozens of people saying that they can't get a date, or that their mate is unsatisfactory and so on. So to the OP I'd say: if this family member wants this, let this family member go for it. It takes that motivation at the very least. If that motivation is there then the hard work (and even the rejections and blips along the road) are worth it. If not, then there's no need to force it. Many people live without mates and are perfectly happy.