Catholic art does not have a canon. An artist is free to make any image he can, from cheaply sentimental to blasphemous. Some of it finds its way into churches. That is very unfortunate, but for that reason you cannot point out to any particular piece of art, vaguely suggestive of Catholicism, and project a Catholic doctrine from it.
Mary with infant Jesus on the cross with adult Jesus is something quite unique. There are many traditional ways to depict the intimacy that exists between Jesus and His mother but this is not one of them. What we have here is one, unique case of artistic license. I have seen much worse.
Were it depicting Mary as actually physically crucified, -- attached to the cross with nails or ropes like Jesus is,-- I would have a serious problem with this cross. As it is, with Mary floating in the air, it simply conveys the perfectly Catholic idea that Mary -- and in fact all faithful Christians -- participate in the suffering of Christ.
[I, St. Paul] rejoice in my sufferings for you, and fill up those things that are wanting of the sufferings of Christ, in my flesh, for his body, which is the church. (Colossians 1:24)
It is admirable that you can be somewhat candid in putting the best face on it.
Thanks.